Why is my ps3 freezing?

I've only had a PS3 for about 6 months now, but it already has had problems. When I play my NBA 2k11, after an hour or so, I quit then it freezes and then restarts itself. Then inFamous just freezes randomly anywhere in the game. I havent tried my other games yet, because I'm afraid to. I don't think it is overheating because when I feel it, it is just warm, and I can't even hear the fan unless I put my ear right on the PS3.