My pc keeps crashing and then rebooting

[Hymirth]

Hi I built my rig about 1 month ago and everything has been going fine until a couple of days ago. My PC has started randomly crashing then rebooting. This can happen after 10 minutes or after 3 hours, but it appears to be getting more regular. I'm kind of stuck on this because there are so many possible reasons - at least in my naive eyes - for this to happen.

I'm using:
AsRock 990FX Extreme3 Motherboard
AMD FX8320 Black Edition 8 Core
AMD radeon hd 7850

 

[cin19]

It maybe the MB, because the MB has only 4+1 power phase (VRM) and the fx8320 has TDP125W, even you don't OC the cpu, the MB will work hard to keep up the fx8320 over time the MB maybe overhead because the power phase counts is lower. Check out the link, both 970 extreme3 and 990 extreme3 have same counts. https://spreadsheets.google.com/spreadsheet/pub?key=0AgN1D79Joo7tdE9xMUFlMEVWeFhuckJEVF9aMmtpUFE&gid=2

So you can try this to see the problem is from MB or not. Try to unclock the CPU frequency by going to the BIOS, to change the setting. Check the manual. And run the PC to see the PC does crash or not.