The z77's are particularly ornery when it comes to BIOS recovery. Hav't looked at your board yet, but here are some questions/suggestions.
-You've tried unsuccessfully to force boot from the back up BIOS?
-Try CLR_CMOS - Disconnect power from board, but leave BATT installed then short jumper
-Does your board have a flash back button the rear panel?
-Remove all but one stick of RAM
-Try boot and hold ALT, then try rapidly tapping F10
This is tough to recover from on this chipset. Let us know your results/answers.