Do you know if you were running Windows 8 as UEFI or in a secure boot mode?
If you do have your bios set up for UEFI, the DVD maker will not create a bootable Windows 7 version for UEFI. You might want to change the bios settings, or try making the Flash Drive again. I normally just use Diskpart to set up the drive, then copy the files from the .iso over. If you can't copy them, you might just burn a DVD and use that or load the DVD and then copy the files.
But make sure you are using the boot device menu and choosing the version of the flash drive you want to boot.