Computer randomly crashes while playing (Battlefield 3, CS:GO, others)

[Fuumy]

My desktop keeps restarting for no apparent reason. It's a gaming desktop--well, as close to one as I've had these last two years, because much of it is sort of old but still runs smoothly enough--and I recently reinstalled Windows 7 to see if that solved the issue, but it didn't. I'll be playing a game and suddenly the computer just crashes. All of my drivers are up to date, I've updated the BIOS in the motherboard, and also updated Windows. I still can't seem to find the issue. I'm pretty sure it's a hardware issue, probably something with the motherboard because the USB ports act weird at random times; I ran a diagnostic test and it came back with no results. Can anyone help me? I don't know what specs you would need to figure this out but would be happy to provide anything.

Thanks a lot for any help. I'm familiar with computers but not really a techie at all so I can't find the issue...

 

[AddRAM]

What are the cpu and gpu temps ?

Nothing out of the ordinary ?

 

[Fuumy]

My CPU averages at 17 C (62 F) and my GPU averages at 39 C (102 F). I've never monitored them sadly, so I don't know if this is normal...

 

[AddRAM]

They are good for averages but you need to know your temps right before a crash, I know, hard to do.

 

[Fuumy]

I'll start monitoring them in the morning, and load the game and see when it crashes. I'll let you know what I can find, thanks.