Flashing backup bios while overclocked can be fatal. Because if something goes wrong with an overclock, it automatically loads the backup BIOS even if everything is fine with the primary bios. And if it can't access the backup BIOS it will loop forever.

Try NINJA Pressing Alt-F12 and keep mashing it, to see if you can get it to boot from the primary BIOS. I know that pressing it 3 times switches from primary to backup (makes backup primary), but you might not be even given a chance to do that if the board won't stay on long enough....