My friend's PC just started boot looping after working perfectly fine for the past 6 months, sometimes not even being able to enter BIOS before rebooting, and sometimes lasting 2 minutes turned on in windows. I have tried re-seating the RAM, using the on-board GPU, unplugging and re-plugging every cable, checked that all the fans are spinning properly and checked for a sign or smell of burning. Nothing. Everything looked OK. Prior to this the PC was on doing basic tasks all day. What could be the issue? My guess is either the Motherboard or the PSU, unfortunately i cannot test any of these since I don't have the hardware on-hand. What should I do next? Thanks.

Specs: Mobo: ASrock h61m-dgs PSU: OCZ ZS 80 bronze 750 watt CPU: i5-3450 RAM: 8gb Kingston low profile 1333mhz GPU: EVGA GTX 670 4GB