Hi AWarGuy,
I need you to check to see what version of ComboFix you have. To do this, right click on ComboFix.exe > Properties > Details tab. If it's not 12-05-21.03 or later, then delete it and download it again.
Then run ComboFix. If it gets terminated while installing, restart your computer and run it again right away.
Got the updated version, did it right away and no luck. Should I consider reformatting my PC? If so, I fear that the virus may spread onto my external hard drive, would that happen?
Reformatting your PC would probably be the easiest and safest option. ZeroAccess does not spread to removable media so don't worry about your external HD.