Long story short, I messed with overclocking my AMD Radeon HD6770 and it locked up my PC every time I booted. Microsoft in their infinite wisdom decided to remove the F8 safe-mode functionality in Windows 8 so the only way to access safe mode is to interrupt [power off] the boot process, which brings up the auto-repair system. Why Microsoft removed the F8 functionality is beyond me!
I went through many more steps than I am going to describe here; you don’t need to be bored with the full tedious process. What you need to do is power off during boot up; power back on and select “advanced repair options” >>> “troubleshoot”, >>> “advanced options” >>> “Windows startup settings” and finally “restart”. When your PC restarts; press F4 or F5 to enter safe-mode.
Once booted into safe-mode, navigate to “C:\Users\<-username->\appdata\local\ATI\ACE” and delete the three files in the ACE directory; these files will be recreated when you reboot your computer, the appdata directory is hidden, so you’ll need to check the “Hidden Items” box on the view tab to see it. Reboot and everything is reset to defaults in Catalyst Control Center, so you can try to overclock again or like me, leave well enough alone, I’ll never get those two hours back!
Hopefully this little bit of advice will help you not have to spend two or more hours try to find a fix!