Can't access all RAM

I have an ASUS P6T Deluxe V2, BIOS version 1202 (latest) with an i7 920 and I try to install 24GB RAM, which consists in two sets of Corsair Vengeance 12GB-Triple-Channel-DDR3-Memory-Kit (i.e. 2 kits oer set of 3 x 4GB, PC3-12800 (1600MHz), 9-9-9-24, 1.5V).

The BIOS detects only 16GB, although I have read that should work to full 24GB.

Below I see that two slots seem unoccupied. I have tried the memory sets separately, they work.

What could be the reason, how could I diagnose?

Thank you.

# dmidecode 3.1
Getting SMBIOS data from sysfs.
SMBIOS 2.5 present.
81 structures occupying 3016 bytes.
Table at 0x000F0700.

Handle 0x0000, DMI type 0, 24 bytes
BIOS Information
    Vendor: American Megatrends Inc.
    Version: 1202   
    Release Date: 12/22/2010
    Address: 0xF0000
    Runtime Size: 64 kB
    ROM Size: 2048 kB
    Characteristics:
        ISA is supported
        PCI is supported
        PNP is supported
        APM is supported
        BIOS is upgradeable
        BIOS shadowing is allowed
        ESCD support is available
        Boot from CD is supported
        Selectable boot is supported
        BIOS ROM is socketed
        EDD is supported
        5.25"/1.2 MB floppy services are supported (int 13h)
        3.5"/720 kB floppy services are supported (int 13h)
        3.5"/2.88 MB floppy services are supported (int 13h)
        Print screen service is supported (int 5h)
        8042 keyboard services are supported (int 9h)
        Serial services are supported (int 14h)
        Printer services are supported (int 17h)
        CGA/mono video services are supported (int 10h)
        ACPI is supported
        USB legacy is supported
        LS-120 boot is supported
        ATAPI Zip drive boot is supported
        BIOS boot specification is supported
        Targeted content distribution is supported
    BIOS Revision: 8.15

Handle 0x0001, DMI type 1, 27 bytes
System Information
    Manufacturer: System manufacturer
    Product Name: System Product Name
    Version: System Version
    Serial Number: System Serial Number
    UUID: C0AE001E-8C00-01B9-2C22-00248C0B825A
    Wake-up Type: Power Switch
    SKU Number: To Be Filled By O.E.M.
    Family: To Be Filled By O.E.M.

Handle 0x0002, DMI type 2, 15 bytes
Base Board Information
    Manufacturer: ASUSTeK Computer INC.
    Product Name: P6T DELUXE V2
    Version: Rev 1.xx
    Serial Number: MS1C91B00100276
    Asset Tag: To Be Filled By O.E.M.
    Features:
        Board is a hosting board
        Board is replaceable
    Location In Chassis: To Be Filled By O.E.M.
    Chassis Handle: 0x0003
    Type: Motherboard
    Contained Object Handles: 0

Handle 0x0003, DMI type 3, 21 bytes
Chassis Information
    Manufacturer: Chassis Manufacture
    Type: Desktop
    Lock: Not Present
    Version: Chassis Version
    Serial Number: Chassis Serial Number
    Asset Tag: Asset-1234567890
    Boot-up State: Safe
    Power Supply State: Safe
    Thermal State: Safe
    Security Status: None
    OEM Information: 0x00000001
    Height: Unspecified
    Number Of Power Cords: 1
    Contained Elements: 0

Handle 0x0004, DMI type 4, 40 bytes
Processor Information
    Socket Designation: LGA1366
    Type: Central Processor
    Family: Core i7
    Manufacturer: Intel            
    ID: A4 06 01 00 FF FB EB BF
    Signature: Type 0, Family 6, Model 26, Stepping 4
    Flags:
        FPU (Floating-point unit on-chip)
        VME (Virtual mode extension)
        DE (Debugging extension)
        PSE (Page size extension)
        TSC (Time stamp counter)
        MSR (Model specific registers)
        PAE (Physical address extension)
        MCE (Machine check exception)
        CX8 (CMPXCHG8 instruction supported)
        APIC (On-chip APIC hardware supported)
        SEP (Fast system call)
        MTRR (Memory type range registers)
        PGE (Page global enable)
        MCA (Machine check architecture)
        CMOV (Conditional move instruction supported)
        PAT (Page attribute table)
        PSE-36 (36-bit page size extension)
        CLFSH (CLFLUSH instruction supported)
        DS (Debug store)
        ACPI (ACPI supported)
        MMX (MMX technology supported)
        FXSR (FXSAVE and FXSTOR instructions supported)
        SSE (Streaming SIMD extensions)
        SSE2 (Streaming SIMD extensions 2)
        SS (Self-snoop)
        HTT (Multi-threading)
        TM (Thermal monitor supported)
        PBE (Pending break enabled)
    Version: Intel(R) Core(TM) i7 CPU 920 @ 2.67GHz              
    Voltage: 1.2 V
    External Clock: 133 MHz
    Max Speed: 2666 MHz
    Current Speed: 2666 MHz
    Status: Populated, Enabled
    Upgrade: Other
    L1 Cache Handle: 0x0005
    L2 Cache Handle: 0x0006
    L3 Cache Handle: 0x0007
    Serial Number: To Be Filled By O.E.M.
    Asset Tag: To Be Filled By O.E.M.
    Part Number: To Be Filled By O.E.M.
    Core Count: 4
    Core Enabled: 4
    Thread Count: 8
    Characteristics:
        64-bit capable

Handle 0x0005, DMI type 7, 19 bytes
Cache Information
    Socket Designation: L1-Cache
    Configuration: Enabled, Not Socketed, Level 1
    Operational Mode: Write Through
    Location: Internal
    Installed Size: 256 kB
    Maximum Size: 256 kB
    Supported SRAM Types:
        Other
    Installed SRAM Type: Other
    Speed: Unknown
    Error Correction Type: Parity
    System Type: Instruction
    Associativity: 4-way Set-associative

Handle 0x0006, DMI type 7, 19 bytes
Cache Information
    Socket Designation: L2-Cache
    Configuration: Enabled, Not Socketed, Level 2
    Operational Mode: Write Through
    Location: Internal
    Installed Size: 1024 kB
    Maximum Size: 1024 kB
    Supported SRAM Types:
        Other
    Installed SRAM Type: Other
    Speed: Unknown
    Error Correction Type: Single-bit ECC
    System Type: Unified
    Associativity: 8-way Set-associative

Handle 0x0007, DMI type 7, 19 bytes
Cache Information
    Socket Designation: L3-Cache
    Configuration: Enabled, Not Socketed, Level 3
    Operational Mode: Write Back
    Location: Internal
    Installed Size: 8192 kB
    Maximum Size: 8192 kB
    Supported SRAM Types:
        Other
    Installed SRAM Type: Other
    Speed: Unknown
    Error Correction Type: Single-bit ECC
    System Type: Unified
    Associativity: 16-way Set-associative

Handle 0x0008, DMI type 5, 28 bytes
Memory Controller Information
    Error Detecting Method: 64-bit ECC
    Error Correcting Capabilities:
        None
    Supported Interleave: One-way Interleave
    Current Interleave: One-way Interleave
    Maximum Memory Module Size: 4096 MB
    Maximum Total Memory Size: 24576 MB
    Supported Speeds:
        70 ns
        60 ns
    Supported Memory Types:
        DIMM
        SDRAM
    Memory Module Voltage: 3.3 V
    Associated Memory Slots: 6
        0x0009
        0x000A
        0x000B
        0x000C
        0x000D
        0x000E
    Enabled Error Correcting Capabilities:
        None

Handle 0x0009, DMI type 6, 12 bytes
Memory Module Information
    Socket Designation: DIMM0
    Bank Connections: 1
    Current Speed: 1 ns
    Type: DIMM
    Installed Size: 4096 MB (Single-bank Connection)
    Enabled Size: 4096 MB (Single-bank Connection)
    Error Status: OK

Handle 0x000A, DMI type 6, 12 bytes
Memory Module Information
    Socket Designation: DIMM1
    Bank Connections: 2
    Current Speed: 1 ns
    Type: DIMM
    Installed Size: 4096 MB (Single-bank Connection)
    Enabled Size: 4096 MB (Single-bank Connection)
    Error Status: OK

Handle 0x000B, DMI type 6, 12 bytes
Memory Module Information
    Socket Designation: DIMM2
    Bank Connections: 3
    Current Speed: 1 ns
    Type: DIMM
    Installed Size: 4096 MB (Single-bank Connection)
    Enabled Size: 4096 MB (Single-bank Connection)
    Error Status: OK

Handle 0x000C, DMI type 6, 12 bytes
Memory Module Information
    Socket Designation: DIMM3
    Bank Connections: 4
    Current Speed: 1 ns
    Type: DIMM
    Installed Size: 4096 MB (Single-bank Connection)
    Enabled Size: 4096 MB (Single-bank Connection)
    Error Status: OK

Handle 0x000D, DMI type 6, 12 bytes
Memory Module Information
    Socket Designation: DIMM4
    Bank Connections: 0 0
    Current Speed: Unknown
    Type: Unknown
    Installed Size: Not Installed
    Enabled Size: Not Installed
    Error Status: OK

Handle 0x000E, DMI type 6, 12 bytes
Memory Module Information
    Socket Designation: DIMM5
    Bank Connections: 0 0
    Current Speed: Unknown
    Type: Unknown
    Installed Size: Not Installed
    Enabled Size: Not Installed
    Error Status: OK

Handle 0x000F, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: PS/2 Keyboard
    Internal Connector Type: None
    External Reference Designator: PS/2 Keyboard
    External Connector Type: PS/2
    Port Type: Keyboard Port

Handle 0x0010, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: USB12
    Internal Connector Type: None
    External Reference Designator: USB12
    External Connector Type: Access Bus (USB)
    Port Type: USB

Handle 0x0011, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: USB34
    Internal Connector Type: None
    External Reference Designator: USB34
    External Connector Type: Access Bus (USB)
    Port Type: USB

Handle 0x0012, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: USB56
    Internal Connector Type: None
    External Reference Designator: USB56
    External Connector Type: Access Bus (USB)
    Port Type: USB

Handle 0x0013, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: USB78
    Internal Connector Type: None
    External Reference Designator: USB78
    External Connector Type: Access Bus (USB)
    Port Type: USB

Handle 0x0014, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: IE1394_1
    Internal Connector Type: None
    External Reference Designator: IEEE1394 1
    External Connector Type: IEEE 1394
    Port Type: Firewire (IEEE P1394)

Handle 0x0015, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: ESATA
    Internal Connector Type: None
    External Reference Designator: ESATA
    External Connector Type: IEEE 1394
    Port Type: SATA

Handle 0x0016, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: LAN1
    Internal Connector Type: None
    External Reference Designator: GbE LAN 1
    External Connector Type: RJ-45
    Port Type: Network Port

Handle 0x0017, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: LAN2
    Internal Connector Type: None
    External Reference Designator: GbE LAN 2
    External Connector Type: RJ-45
    Port Type: Network Port

Handle 0x0018, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: AUDIO
    Internal Connector Type: None
    External Reference Designator: AUDIO
    External Connector Type: Other
    Port Type: Audio Port

Handle 0x0019, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: Audio Line Out1
    Internal Connector Type: None
    External Reference Designator: Audio Line Out1
    External Connector Type: Mini Jack (headphones)
    Port Type: Audio Port

Handle 0x001A, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: Audio Line Out2
    Internal Connector Type: None
    External Reference Designator: Audio Line Out2
    External Connector Type: Mini Jack (headphones)
    Port Type: Audio Port

Handle 0x001B, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: Audio Line Out3
    Internal Connector Type: None
    External Reference Designator: Audio Line Out3
    External Connector Type: Mini Jack (headphones)
    Port Type: Audio Port

Handle 0x001C, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: Audio Line Out4
    Internal Connector Type: None
    External Reference Designator: Audio Line Out4
    External Connector Type: Mini Jack (headphones)
    Port Type: Audio Port

Handle 0x001D, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: Audio Line Out5
    Internal Connector Type: None
    External Reference Designator: Audio Line Out5
    External Connector Type: Mini Jack (headphones)
    Port Type: Audio Port

Handle 0x001E, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: Audio Line Out6
    Internal Connector Type: None
    External Reference Designator: Audio Line Out6
    External Connector Type: Mini Jack (headphones)
    Port Type: Audio Port

Handle 0x001F, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: SATA1
    Internal Connector Type: SAS/SATA Plug Receptacle
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: SATA

Handle 0x0020, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: SATA2
    Internal Connector Type: SAS/SATA Plug Receptacle
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: SATA

Handle 0x0021, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: SATA3
    Internal Connector Type: SAS/SATA Plug Receptacle
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: SATA

Handle 0x0022, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: SATA4
    Internal Connector Type: SAS/SATA Plug Receptacle
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: SATA

Handle 0x0023, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: SATA5
    Internal Connector Type: SAS/SATA Plug Receptacle
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: SATA

Handle 0x0024, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: SATA6
    Internal Connector Type: SAS/SATA Plug Receptacle
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: SATA

Handle 0x0025, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: SAS1
    Internal Connector Type: SAS/SATA Plug Receptacle
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: SATA

Handle 0x0026, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: SAS2
    Internal Connector Type: SAS/SATA Plug Receptacle
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: SATA

Handle 0x0027, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: PRI_EIDE
    Internal Connector Type: SAS/SATA Plug Receptacle
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: SATA

Handle 0x0028, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: FLOPPY
    Internal Connector Type: On Board Floppy
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: Other

Handle 0x0029, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: USB910
    Internal Connector Type: Access Bus (USB)
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: USB

Handle 0x002A, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: USB1112
    Internal Connector Type: Access Bus (USB)
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: USB

Handle 0x002B, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: USB1314
    Internal Connector Type: Access Bus (USB)
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: USB

Handle 0x002C, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: IE1394_2
    Internal Connector Type: IEEE 1394
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: Firewire (IEEE P1394)

Handle 0x002D, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: CD
    Internal Connector Type: On Board Sound Input From CD-ROM
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: Audio Port

Handle 0x002E, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: AAFP
    Internal Connector Type: Mini Jack (headphones)
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: Audio Port

Handle 0x002F, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: CPU_FAN
    Internal Connector Type: Other
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: Other

Handle 0x0030, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: PWR_FAN
    Internal Connector Type: Other
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: Other

Handle 0x0031, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: CHA_FAN1
    Internal Connector Type: Other
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: Other

Handle 0x0032, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: CHA_FAN2
    Internal Connector Type: Other
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: Other

Handle 0x0033, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: CHA_FAN3
    Internal Connector Type: Other
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: Other

Handle 0x0034, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: SPDIF_OUT
    Internal Connector Type: On Board Sound Input From CD-ROM
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: Audio Port

Handle 0x0035, DMI type 8, 9 bytes
Port Connector Information
    Internal Reference Designator: FP_AUDIO
    Internal Connector Type: On Board Sound Input From CD-ROM
    External Reference Designator: Not Specified
    External Connector Type: None
    Port Type: Audio Port

Handle 0x0036, DMI type 9, 13 bytes
System Slot Information
    Designation: PCIEX4_1
    Type: 32-bit PCI Express
    Current Usage: Available
    Length: Short
    ID: 1
    Characteristics:
        3.3 V is provided
        Opening is shared
        PME signal is supported

Handle 0x0037, DMI type 9, 13 bytes
System Slot Information
    Designation: PCIEX16_1
    Type: 32-bit PCI Express
    Current Usage: In Use
    Length: Short
    ID: 2
    Characteristics:
        3.3 V is provided
        Opening is shared
        PME signal is supported

Handle 0x0038, DMI type 9, 13 bytes
System Slot Information
    Designation: PCI1
    Type: 32-bit PCI
    Current Usage: Available
    Length: Short
    ID: 3
    Characteristics:
        3.3 V is provided
        Opening is shared
        PME signal is supported

Handle 0x0039, DMI type 9, 13 bytes
System Slot Information
    Designation: PCI2
    Type: 32-bit PCI
    Current Usage: Available
    Length: Short
    ID: 4
    Characteristics:
        3.3 V is provided
        Opening is shared
        PME signal is supported

Handle 0x003A, DMI type 9, 13 bytes
System Slot Information
    Designation: PCIEX16_2
    Type: 32-bit PCI Express
    Current Usage: In Use
    Length: Short
    ID: 5
    Characteristics:
        3.3 V is provided
        Opening is shared
        PME signal is supported

Handle 0x003B, DMI type 9, 13 bytes
System Slot Information
    Designation: PCIEX16_3
    Type: 32-bit PCI Express
    Current Usage: Available
    Length: Short
    ID: 6
    Characteristics:
        3.3 V is provided
        Opening is shared
        PME signal is supported

Handle 0x003C, DMI type 10, 6 bytes
On Board Device Information
    Type: Ethernet
    Status: Enabled
    Description:  Onboard Ethernet

Handle 0x003D, DMI type 11, 5 bytes
OEM Strings
    String 1: To Be Filled By O.E.M.
    String 2: To Be Filled By O.E.M.
    String 3: To Be Filled By O.E.M.
    String 4: To Be Filled By O.E.M.

Handle 0x003E, DMI type 13, 22 bytes
BIOS Language Information
    Language Description Format: Long
    Installable Languages: 6
        en|US|iso8859-1
        zh|ZH|iso8859-1
        de|DE|iso8859-1
        cn|CN|iso8859-1
        fr|FR|iso8859-1
        ja|JP|unicode-1
    Currently Installed Language: en|US|iso8859-1

Handle 0x003F, DMI type 15, 55 bytes
System Event Log
    Area Length: 1008 bytes
    Header Start Offset: 0x2010
    Data Start Offset: 0x2010
    Access Method: OEM-specific
    Access Address: Unknown
    Status: Valid, Not Full
    Change Token: 0x00000000
    Header Format: No Header
    Supported Log Type Descriptors: 1
    Descriptor 1: OEM-specific
    Data Format 1: POST results bitmap

Handle 0x0040, DMI type 16, 15 bytes
Physical Memory Array
    Location: System Board Or Motherboard
    Use: System Memory
    Error Correction Type: Multi-bit ECC
    Maximum Capacity: 24 GB
    Error Information Handle: Not Provided
    Number Of Devices: 6

Handle 0x0041, DMI type 19, 15 bytes
Memory Array Mapped Address
    Starting Address: 0x00000000000
    Ending Address: 0x000000003FF
    Range Size: 1 kB
    Physical Array Handle: 0x0040
    Partition Width: 1

Handle 0x0042, DMI type 17, 27 bytes
Memory Device
    Array Handle: 0x0040
    Error Information Handle: Not Provided
    Total Width: 72 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: DIMM
    Set: None
    Locator: DIMM0
    Bank Locator: BANK0
    Type: Other
    Type Detail: Other
    Speed: 1066 MT/s
    Manufacturer: Manufacturer00
    Serial Number: SerNum00
    Asset Tag: AssetTagNum0
    Part Number: ModulePartNumber00

Handle 0x0043, DMI type 20, 19 bytes
Memory Device Mapped Address
    Starting Address: 0x00000000000
    Ending Address: 0x000000003FF
    Range Size: 1 kB
    Physical Device Handle: 0x0042
    Memory Array Mapped Address Handle: 0x0041
    Partition Row Position: 1
    Interleave Position: Unknown
    Interleaved Data Depth: 2

Handle 0x0044, DMI type 17, 27 bytes
Memory Device
    Array Handle: 0x0040
    Error Information Handle: Not Provided
    Total Width: 72 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: DIMM
    Set: None
    Locator: DIMM1
    Bank Locator: BANK1
    Type: Other
    Type Detail: Other
    Speed: 1066 MT/s
    Manufacturer: Manufacturer01
    Serial Number: SerNum01
    Asset Tag: AssetTagNum1
    Part Number: ModulePartNumber01

Handle 0x0045, DMI type 20, 19 bytes
Memory Device Mapped Address
    Starting Address: 0x00000000000
    Ending Address: 0x000000003FF
    Range Size: 1 kB
    Physical Device Handle: 0x0044
    Memory Array Mapped Address Handle: 0x0041
    Partition Row Position: 1
    Interleave Position: Unknown
    Interleaved Data Depth: 2

Handle 0x0046, DMI type 17, 27 bytes
Memory Device
    Array Handle: 0x0040
    Error Information Handle: Not Provided
    Total Width: 72 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: DIMM
    Set: None
    Locator: DIMM2
    Bank Locator: BANK2
    Type: Other
    Type Detail: Other
    Speed: 1066 MT/s
    Manufacturer: Manufacturer02
    Serial Number: SerNum02
    Asset Tag: AssetTagNum2
    Part Number: ModulePartNumber02

Handle 0x0047, DMI type 20, 19 bytes
Memory Device Mapped Address
    Starting Address: 0x00000000000
    Ending Address: 0x000000003FF
    Range Size: 1 kB
    Physical Device Handle: 0x0046
    Memory Array Mapped Address Handle: 0x0041
    Partition Row Position: 1
    Interleave Position: Unknown
    Interleaved Data Depth: 2

Handle 0x0048, DMI type 17, 27 bytes
Memory Device
    Array Handle: 0x0040
    Error Information Handle: Not Provided
    Total Width: 72 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: DIMM
    Set: None
    Locator: DIMM3
    Bank Locator: BANK3
    Type: Other
    Type Detail: Other
    Speed: 1066 MT/s
    Manufacturer: Manufacturer03
    Serial Number: SerNum03
    Asset Tag: AssetTagNum3
    Part Number: ModulePartNumber03

Handle 0x0049, DMI type 20, 19 bytes
Memory Device Mapped Address
    Starting Address: 0x00000000000
    Ending Address: 0x000000003FF
    Range Size: 1 kB
    Physical Device Handle: 0x0048
    Memory Array Mapped Address Handle: 0x0041
    Partition Row Position: 1
    Interleave Position: Unknown
    Interleaved Data Depth: 2

Handle 0x004A, DMI type 17, 27 bytes
Memory Device
    Array Handle: 0x0040
    Error Information Handle: Not Provided
    Total Width: 72 bits
    Data Width: 64 bits
    Size: No Module Installed
    Form Factor: DIMM
    Set: None
    Locator: DIMM4
    Bank Locator: BANK4
    Type: Other
    Type Detail: Other
    Speed: Unknown
    Manufacturer: Manufacturer04
    Serial Number: SerNum04
    Asset Tag: AssetTagNum4
    Part Number: ModulePartNumber04

Handle 0x004B, DMI type 20, 19 bytes
Memory Device Mapped Address
    Starting Address: 0x00000000000
    Ending Address: 0x000000003FF
    Range Size: 1 kB
    Physical Device Handle: 0x004A
    Memory Array Mapped Address Handle: 0x0041
    Partition Row Position: 1
    Interleave Position: Unknown
    Interleaved Data Depth: 2

Handle 0x004C, DMI type 17, 27 bytes
Memory Device
    Array Handle: 0x0040
    Error Information Handle: Not Provided
    Total Width: 72 bits
    Data Width: 64 bits
    Size: No Module Installed
    Form Factor: DIMM
    Set: None
    Locator: DIMM5
    Bank Locator: BANK5
    Type: Other
    Type Detail: Other
    Speed: Unknown
    Manufacturer: Manufacturer05
    Serial Number: SerNum05
    Asset Tag: AssetTagNum5
    Part Number: ModulePartNumber05

Handle 0x004D, DMI type 20, 19 bytes
Memory Device Mapped Address
    Starting Address: 0x00000000000
    Ending Address: 0x000000003FF
    Range Size: 1 kB
    Physical Device Handle: 0x004C
    Memory Array Mapped Address Handle: 0x0041
    Partition Row Position: 1
    Interleave Position: Unknown
    Interleaved Data Depth: 2

Handle 0x004E, DMI type 32, 20 bytes
System Boot Information
    Status: No errors detected

Handle 0x004F, DMI type 139, 54 bytes
OEM-specific Type
    Header and Data:
        8B 36 4F 00 00 1E 8C 00 01 B9 2C 22 04 04 32 55
        F8 00 A2 02 A1 00 40 63 43 10 FE 81 03 DF 40 B2
        00 20 00 73 3C 10 08 00 00 00 00 00 00 00 00 00
        00 00 00 00 00 01
    Strings:
        V1394GUID

Handle 0x0050, DMI type 127, 4 bytes
End Of Table

I have tried many tricks in the BIOS, including setting manually memory parameters to be exactly as specified by the vendor, but no avail. Eventually, I have switched the kits in their slots and worked, it recognizes all the 24GB of RAM. Memtest did not show errors after 3 steps of checking. I know it is not a solution working in all the cases, but worked in my case.