It was last night that I first noticed a problem. I was playing Warcraft (world of) and my computer suddenly rebooted, my current system has never had any such problems so I discarded it as a freak one-off occurance. Thirty minutes later the same thing happened, it was at this point I went to bed, slightly worried about the health of my computer (I even turned it off!). Today I booted up my machine and noticed it faultered and failed to boot, rebooting itself once or twice before finally settling down and completing the boot sequence. Rather haphazardly I loaded up Warcraft... it seemed to be OK, and everything was running smoothly for about 30 minutes, but then came the familar sound of my monitor pinging off and back on, it had restarted again. It should be noted none of these restarts were preceeded by any blue screens of death or other error messages of any kind (and I have the automatically reboot on system failure option turned off). It was because of this I think I began to fear the worst; some kind of hardware malfunction, and because this problem seemed to be exclusively associated with the running of computer games I feared for my graphics card. It was at this point I decided to check the cooling fan on the card for dust or any obstructions that could be causing the card to overheat. I noticed that the card itself was quite hot, but I was unsure how to view the temperature exactly (I think most of the new cards come with thermometers...?). I left the computer turned off for ~2 hours till everything had cooled down. I booted it back up and attempted to play Warcraft, it got to the loading screen, fully loaded the game and just as it was about to display the graphics it rebooted. When it had finished booting up (again) I tried to play Half-life 2 (another game I have had no trouble playing in the past), it got to the loading screen, loaded for a few seconds and then exited to my desktop (but did not reboot this time). Still rather confused I downloaded the latest drivers (catalyst) from the ATI site. The drivers would begin to install and the ATI logo would appear in full screen before my machine would reboot. I decided to follow this guide: http://www.tweakguides.com/ATICAT_4.html to avoid experiencing any problems replacing the old drivers with new drivers which I had read about before. No luck. Exactly the same thing happened; the install would begin and the ATI logo would appear and the machine would instantly reboot. At this point I am pretty much out of ideas as to what the problem is exactly or how to solve it. Any help/wisdom would be greatly appreciated. The card in question is a Radeon X800 Pro made by Sapphire. I have a 1.85 gigahertz AMD Athlon XP processor. My motherboard is and Nvidia Nforce 2 made by Epox. I am running Windows XP Professional.