I have ECS Z77H2-A3 board installed with windows 8 pro. everything working fine.
Later i try update the latest bios to properly support windows 8 and that's the begin from the trouble.
now i can't shutdown my pc anymore. when i try shutdown the system. after couple second my monitor turn off except my pc still running. tried disable fast shutdown option on power configuration did't help too.
I'm sure you tried this but just in case...and I'm just taking a stab at this...
If you are hitting the case power button to shut the system down your power button options may have changed (possibly in bios) so that hitting it is causeing some kind of standby or sleep mode instead of powering off.
it a bios glitch i had the same issue with my asus mb. the fix is easy. just unplug the pc from the wall let the mb drain and then clear the cmos. then go back in and set the bios back to factory default and your pc should shut down right.