Random computer crashes while playing games.

Hello there, I recently built a new PC(less than a week ago.) and I am experiencing some weird freezing while playing games. This isn't a problem specific to any one game and seems to happen randomly. I have read some of the other posts that seem to have the same problems I have but they are dealing with older PCs.

Basically what happens is while playing the game suddenly freezes and the monitor acts as if the computer has gone into sleep mode. I can hear the sound of the game for a bit before it also stops as well. The computer will no longer respond to anything and the only way to get out of it is to hit the reset button or turn it on/off. The thing is this doesn't happen regularly, like 30mins into the game or something. Sometimes I can play a game for hours and nothing happens, other times I can just be playing for an hour or less and it crashes.

The only thing I can come up with myself is that it is the GPU in some way, it is the only part that is left over from my old PC(saving up to buy a new one.) and this problem happened with my old PC as well. Since this is the only common factor between the PCs(besides the OS of course.), it is making me think its a GPU problem.

So I have a couple of questions.

#1: Antyhing I can do to prevent the crashes?

#2: If the problem can't be fixed without replacing the GPU, will these crashes every now and then cause long term problms before I get a new GPU?

Specs:
AMD FX 6100 3.30GHz
8gb DDR3 RAM
500gb Seagate Barracuda
Nvidia GeForce 8800GTS
Windows 7 Pro 64-bit
Asus M5A97 Motherboard
600W Corsair PSU