Try resetting the CMOS which clears your BIOS and rejigs it with default settings. Just an idea. This is exactly what you get when you overclock to an unstable area. It'll tell you how to clear the CMOS in your motherboard manual, but if it doesn't just look about on your mobo for a while for 3 pins with a plastic jumper over only 2 of them. It'll most likely have "CMOS clear" or something written next to in on the board. Move the jumper to the other pin (The one that's not being shorted with the middle) and then after 10 seconds move it back. This should do it. If you can't find it or it doesn't work (It really should) then take the motherboard battery out for a while and this'll do the same job.