Bad software/drivers. Heat. Only way to tell if it's a bad driver, is to shut off the auto restart feature and find out what the error code is. For the heat problem, open the case and clean out the built up dust on the CPU/graphics card/cooling fans. Replace any fan that is not working properly.
I Fixed the restarts but i have another problem. All my games freeze and i would have to turn off the Computer, except for CS:S it just runs slow. PLS Help.
Most likely, a bad system driver. Could be video/sound or chipset. You'll have to uninstall your sound/video drivers and install the latest WHQL versions found from their respective sites. Also, get the latest chipset driver from the chipset manufacturer, not the motherboard site. Install the chipset drivers first, then uninstall/reinstall the newest sound/video. You might even want to update to the latest DirectX 9.0c Decemeber 2006 release.
Okay, So Everything seems in order except for my game, they will freeze up about 5min of play and exit. Now I think its the power, cause i had bought a new VideoCard and it says at least 300Watts and mine is around 280
Did you try attaching the separate power cable to the video card, so that it gets more power? If it's a high-end card, it should probably have a slot. Check the accessories that you got with the card, if there's a power wire supplied with it. I think it should look something like this.
