Checkout sequence
In order of probability
(a) you have a virus
(b) you have a memory failure
(c) you have a fault in the motherboard
(d) you have overheated your CPU
(e) your OS has become corrupted or settings for power management have changed
We need much more detail about your PC and what led up to this. How long has your PC worked. Do you have firewall and anti-virus installed. Have you recently installed something other than proper commercial software. Do you run games. Have you overclocked your PC. Have you been poking around inside the case.