I had to recover mine the other day
for gigabyte z77 without a bios switch you have to hold down front panel pwr switch,then flick on the psu power switch and immediately turn it off,do that around two times then let go of front panel power switch and turn on at psu switch and press front panel power button once
then you should see a message saying recovering main bios with backup bios,once done reboot and update the bios again
bet your board still has a cmos jumper.
neat trick if it works though having to take the side of my case any time I mess up ocing stops me doing it.
unlike when I as younger and used to sit benching 3dmark all day long