To install 7, you need to do a few things (some of which you may have already, based off what I read in your post):
• In BIOS setup, disable UEFI (or enable CSM/Legacy boot).
• After disabling UEFI, disable Secure Boot
• If your disk(s) are setup as GPT disks, you will need to boot to the command line using the Windows 7 disc/disk and convert the drive(s) from GPT to MBR.
Here's a quick guide on converting the drive:
http://www.sevenforums.com/tutorials/26203-convert-gpt-disk-mbr-disk.html
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