Random PC crash, no BSOD dump

Hi There, I have a fairly new PC (approx 12months old) and recently it has been crashing at random times of the day. There is nothing in common with each crash i.e. I am doing different tasks at different times. Basically the PC just turns off and starts booting all over again. There is no BSOD dumps to check and the only thing I see in the event logs before the crash is the Multimedia Class...