It usually is the RAM that has developed a fault. Run memtest[0] to detect errors. Otherwise, in descending order of likelihood, it could be the motherboard, ps

It usually is the RAM that has developed a fault. Run memtest[0] to detect errors. Otherwise, in descending order of likelihood, it could be the motherboard, psu, some driver/kernel crash caused by peripheral, or bad cpu. [0]: http://www.memtest.org/#downiso http://www.memtest.org/#downiso