Cannot run the hand written PE file on Windows7 64 bit

I would like to write my first PE file format (an EXE file) in NASM and run it on Win7 64 bit machine.
This is what I have:

IMAGEBASE equ 0x400000
org IMAGEBASE
bits 32

SECTIONALIGN equ 0x1000
FILEALIGN    equ 0x200

db 'MZ'                       ; e_magic
dw 0                          ; e_cblp 
dw 0                          ; e_cp 
dw 0                          ; e_crlc 
dw 0                          ; e_cparhdr 
dw 0                          ; e_minalloc 
dw 0                          ; e_maxalloc 
dw 0                          ; e_ss 
dw 0                          ; e_sp 
dw 0                          ; e_csum 
dw 0                          ; e_ip 
dw 0                          ; e_cs 
dw 0                          ; e_lsarlc 
dw 0                          ; e_ovno 
times 4 dw 0                  ; e_res 
dw 0                          ; e_oemid 
dw 0                          ; e_oeminfo 
times 10 dw 0                 ; e_res2 
dd PE_SIGNATURE - IMAGEBASE   ; e_lfanew

PE_SIGNATURE:
db 'PE', 0, 0                 ; Signature
dw 0x14c                      ; Machine
dw NUMBEROFSECTIONS           ; NumberOfSections
dd 0                          ; TimeDateStamp
db 0                          ; PointerToSymbolTable
dd 0                          ; NumberOfSymbols
dw SIZEOFOPTIONALHEADER       ; SizeOfOptionalHeader
dw 0x0002 | 0x0100            ; Characteristics

OptionalHeader: 
dw 0x10B                      ; Magic
db 0                          ; MajorLinkerVersion
db 0                          ; MinorLinkerVersion
dd 0                          ; SizeOfCode
dd 0                          ; SizeOfInitializedData
dd 0                          ; SizeOfUninitializedData
dd Start - IMAGEBASE          ; AddressOfEntryPoint
dd Start - IMAGEBASE          ; BaseOfCode
dd DataSection - IMAGEBASE    ; BaseOfData
dd IMAGEBASE                  ; ImageBase
dd SECTIONALIGN               ; SectionAlignment
dd FILEALIGN                  ; FileAlignment
dw 0                          ; MajorOperatingSystemVersion
dw 0                          ; MinorOperatingSystemVersion
dw 0                          ; MajorImageVersion
dw 0                          ; MinorImageVersion
dw 4                          ; MajorSubsystemVersion
dw 0                          ; MinorSubsystemVersion
dd 0                          ; Win32VersionValue
dd 4 * SECTIONALIGN           ; SizeOfImage
dd SIZEOFHEADERS              ; SizeOfHeaders
dd 0                          ; CheckSum
dw 2                          ; Subsystem
dw 0                          ; DllCharacteristics
dd 0                          ; SizeOfStackReserve
dd 0                          ; SizeOfStackCommit
dd 0                          ; SizeOfHeapReserve
dd 0                          ; SizeOfHeapCommit
dd 0                          ; LoaderFlags
dd 16                         ; NumberOfRvaAndSizes

;DataDirectory  
dd 0                          ;ExportsVA        resd 1
dd 0                          ;ExportsSize      resd 1
dd ImpDescriptor - IMAGEBASE  ;ImportsVA        resd 1
dd 0                          ;ImportsSize      resd 1
dd 0                          ;ResourceVA       resd 1
dd 0                          ;ResourceSize     resd 1
dd 0
dd 0                          ;Exception        resd 2
dd 0
dd 0                          ;Security         resd 2
dd 0                          ;FixupsVA         resd 1
dd 0                          ;FixupsSize       resd 1
dd 0                          ;DebugVA          resd 1
dd 0                          ;DebugSize        resd 1
dd 0 
dd 0                          ;Description      resd 2
dd 0
dd 0                          ;MIPS             resd 2
dd 0                          ;TLSVA            resd 1
dd 0                          ;TLSSize          resd 1
dd 0
dd 0                          ;Load             resd 2
dd 0                          ;BoundImportsVA   resd 1
dd 0                          ;BoundImportsSize resd 1
dd 0                          ;IATVA            resd 1
dd 0                          ;IATSize          resd 1
dd 0                          ;DelayImportsVA   resd 1
dd 0                          ;DelayImportsSize resd 1
dd 0
dd 0                          ;COM              resd 2
dd 0
dd 0                          ;reserved         resd 2

SIZEOFOPTIONALHEADER equ $ - OptionalHeader

; section table
SectionHeader:
db '.text', 0, 0, 0           ;Name                    resb 8
dd SECTIONALIGN               ;VirtualSize             resd 1
dd SECTIONALIGN               ;VirtualAddress          resd 1
dd FILEALIGN                  ;SizeOfRawData           resd 1
dd FILEALIGN                  ;PointerToRawData        resd 1
dd 0                          ;PointerToRelocations    resd 1
dd 0                          ;PointerToLinenumbers    resd 1
dw 0                          ;NumberOfRelocations     resw 1
dw 0                          ;NumberOfLinenumbers     resw 1
dd 0x20 | 0x20000000 | 0x40000000 ;Characteristics         resd 1

db '.rdata', 0, 0             ;Name                    resb 8
dd SECTIONALIGN               ;VirtualSize             resd 1
dd 2 * SECTIONALIGN           ;VirtualAddress          resd 1
dd FILEALIGN                  ;SizeOfRawData           resd 1
dd 2 * FILEALIGN              ;PointerToRawData        resd 1
dd 0                          ;PointerToRelocations    resd 1
dd 0                          ;PointerToLinenumbers    resd 1
dw 0                          ;NumberOfRelocations     resw 1
dw 0                          ;NumberOfLinenumbers     resw 1
dd 0x40 | 0x40000000          ;Characteristics         resd 1

db '.data', 0, 0, 0           ;Name                    resb 8
dd SECTIONALIGN               ;VirtualSize             resd 1
dd 3 * SECTIONALIGN           ;VirtualAddress          resd 1
dd FILEALIGN                  ;SizeOfRawData           resd 1
dd 3 * FILEALIGN              ;PointerToRawData        resd 1
dd 0                          ;PointerToRelocations    resd 1
dd 0                          ;PointerToLinenumbers    resd 1
dw 0                          ;NumberOfRelocations     resw 1
dw 0                          ;NumberOfLinenumbers     resw 1
dd 0x40 | 0x40000000 | 0x80000000
NUMBEROFSECTIONS equ ($ - SectionHeader) / 40   
align FILEALIGN, db 0
SIZEOFHEADERS    equ $ - IMAGEBASE

; some aliases
_1 equ IMAGEBASE + SECTIONALIGN
_2 equ IMAGEBASE + 2 * SECTIONALIGN

;code
section progbits vstart=_1 align=FILEALIGN

Start:
mov eax, 0x10
ret

section nobits vstart=_2 align=FILEALIGN
ImpDescriptor:
; kernel32 descriptor
dd 0                          ;OriginalFirstThunk resd 1 ; Characteristics
dd 0                          ;TimeDateStamp  resd 1
dd 0                          ;ForwarderChain resd 1
dd kernel32_name - IMAGEBASE  ;Name1          resd 1
dd 0                          ;FirstThunk     resd 1

; user32 descriptor
dd 0                          ;OriginalFirstThunk resd 1 ; Characteristics
dd 0                          ;TimeDateStamp  resd 1
dd 0                          ;ForwarderChain resd 1
dd user32_name - IMAGEBASE    ;Name1          resd 1
dd 0                          ;FirstThunk     resd 1

; terminator-all-empty descriptor
dd 0                          ;OriginalFirstThunk resd 1 ; Characteristics
dd 0                          ;TimeDateStamp  resd 1
dd 0                          ;ForwarderChain resd 1
dd 0                          ;Name1          resd 1
dd 0                          ;FirstThunk     resd 1

kernel32_name db 'kernel32.dll', 0
user32_name   db 'user32.dll', 0

align FILEALIGN, db 0

;data
DataSection:

;... TODO

align FILEALIGN, db 0

When assembled and created the EXE file, there was no error, but running the program will give the error:
"is not a valid Win32 application."

It would be nice if someone can have a look at the source code and let me know what might be the problem.
Iman.