Try a simple test. Remove the case cover to see if heat is the issue.
Remember that time ages capacitors on the motherboard and power supply. This is why we supersize the power supply so we don't have an issue in a few months.
OK, I've put off dealing with this for awhile for a number of reasons, but I need some help - I'm going into withdrawals! I have an AMD Athlon xp 2000+ processor w/512 ram and a geoforce 440 vidcard computer that I put together myself 14 months ago. I have had ZERO porblems until this past March, when playing any games with 3d graphics caused my computer to shut down and restart. With Civ3, some days I could play for 30 min. before a crash, sometimes 3 hours. Diablo 2 runs for about 10 minutes, then crash. The system only crashes on gaming activities. Internet, DVD and all other functions run fine. I haven't added any new software, nor have there been any upgrades. The Windows error report always says a serious error has occured, but Microsoft says it cannot repair because it is not a Windows error (BTW, I have XP Pro as my OS). Additionally, downloading updated drivers from nVidia has had no effect. I'm assuming that either the vidcard is dead or the cpu is overheating, but as this computer is vital to my wife's business, I'm reluctant to tinker under the hood. Any advice or insight would be helpful.