Pc resetting whilst gaming

Ive had a problem recently where whilst playing a game my pc would just reset. I thought straight away it was overheating but monitoring the temps and nothing goes above 80c cpu or gfx. So now im at a loss as to what could be the cause as all the hardware except the case and psu are under a year old.
Specs:
Intel i5-2500k @ 3.30ghz
asus p8z68-v lx
corsair ddr3 667mhz 4gb x 2
Nvidia geforce gtx 550ti

Any other specs needed just ask.

I recently put in a new hard drive but i tested that for errors and found none. Could windows cause it?