Start the PC. When the POST stalls and you set the "Overclock Failed" message, press the "F1" key - that will take you into BIOS. Don't change anything, just press the "F10" key to save and exit and the PC will reboot. See if that works and post back
Yep I did that and it boots to Windows. I don't get why this message keeps appearing though. It's doing my head in now!!