Computer randomly restarting... how to diagnose the problem?

sheepskin

Honorable
Dec 11, 2013
1
0
10,510
Hello everyone. I was hoping to get a little help with a problem I'm having.

Here's my system
CPU: Intel IvyBridge i5 3570K
MOBO: MSi Z77A-GD65
PSU: AC Power & Cooling Silencer MkII 750W
RAM: 2x Kingston DDR3-1600 4GB
Video card: MSi GeForce 560Ti
SSD: 120GB OCZ Agility 3 (for installing OS which is Windows 7 64-bit)
HDD: 2TB Seagate Barracuda
DVD: Some shitty ASUS thing

I built this computer almost year and a half ago and recently it started acting up. For no reason at all it will completely restart the whole computer. I've tried a bunch of things because I thought it was originally a problem in Windows, but eventually I discovered that was not the case. The computer will sometimes stay on for a while, or sometimes only a few seconds. There is not one specific thing I am doing to make this happen. It will restart in the middle of anything, running any program, starting Windows, or even when I'm in the BIOS. I know it's not overheating because I've checked. I'm thinking it's a PSU or MOBO problem...but I don't really know how to check either of these for any problems. Any advice?