I'm having a strange issue. I have a Gigabyte EP45-UD3L with an E5450 that I just installed, and Windows 8.1 won't boot. This install worked just fine hours ago (had a C2D E5200 in it). It always starts up with "Preparing Automatic Repair" and I managed to catch it giving an "Error Code: 0x000000C4" before automatically rebooting. I just tested and have the same issue with a Windows 8.1 installer USB drive, however a Hiren's Boot CD XP install boots just fine.