Cannot install Windows 7 x64 on my HP Envy

I tried two windows 7 discs, one turned out to be faulty in the software inside (Error 0xc0000185) and the other one keeps giving me some error about some unsigned file in the System32 folder (File: \$WINDOWS~BT\Windows\System32\winload.efi), here are the system informations:

• Windows 8.1 x64,
• Intel Core i7 5500U processor x64,
• 8GB of RAM,
• Nvidia Geforce GTX 850M.

The Laptop is: HP Envy (one of those touchscreen ones), all my drivers are up to date, windows 8.1 is also up to date.

The latest thing I did was (to conserve some of my downloaded data) was partition a disk, that had already some of my files, and the OS files, using one of those third party partition managers.

When I insert my Windows 7 DVD and try installing via the OS UI, it copies the files and unpacks, then reboots the pc, and then it says one of my files are unsigned(mentioned above).

I tried booting directly from the CD, I turn off the computer, access the bios, boot options, set CD/DVD Drive top, exit and save, doesn't boot up from cd and go directly to HDD.

I tried modifying the boot options using the boot manager, there is no option for the CD/DVD Drive.