When I am playing graphics-intensive games like City of Heroes or Tomb Raider: Legend, I quickly start having severe graphics issues. Polygons appear missing, flickering, twisted or stretching in odd directions. If I play for any longer amount of time, random noise covers the screen, and finally the monitor shuts off completely as if it had been disconnected and everything freezes.
The computer is just over a year old and had previously been working fine. The problems started a few weeks ago.
My system specs
Athlon 4200+ dual-core
GeForce 7900 GT
Antec Smartpower 500W PSU
2 GB RAM
* Crashes only ever occur when running graphics-intensive 3D games. Old Tomb Raider II runs without problems, at any time of day. If not playing a game, the computer can run fine for hours.
* Crashes *always* happen in the daytime, and fairly quickly. From about 2 hours after sundown onwards, I can play my games for hours with only a few minor graphics problems. The temperature outside at this time of year is 25-30 C in the daytime and around 18C at night. My room faces East and does not get any direct sunlight after 9 AM or so. We don't have any air conditioning in the house.
* The back fan of the power supply does not start as soon as the computer boots. Rather, it seems to wait until the PSU reaches a certain temperature. I have no idea why. All other fans work just fine.
* The nVidia temperature monitor shows temperatures no higher than the 55C mark, well within tolerance (supposedly).
Things I have already tried:
* Cleaning out all internal fans of dust, including the fan on the card.
* Throttling down my graphics card with Power Strip. From the default 500MHz engine, 750 MHz memory clock, down to 451MHz and 701Mhz, respectively. (And lowering the graphics settings in the games as well.)
* Disconnecting everything, opening the PC case, aiming a fan at the components for 10 minutes until everything is at room temperature. After reconnecting everything, turning the PC on and starting a game, graphics problems started after 5 minutes, crash followed shortly.
* Cooling down the environment of the PC case with standing fans and icepacks. This seems to help a little, but I still get crashes within 20 minutes or so.
I'm kind of at a loss for further things to try and would appreciate any suggestions, or links to better monitoring tools so I can at least pinpoint the problem. Thank you.