I had problems with my 9800Xt restarting my computer...I believe it was heat related. How did I remedy this situation? First of all I'm underpowered 265 Watt max in an old A510 HP computer. That's not the problem. I had the ATI tool installed and had messed around with the settings where the fan was full on most of the time. I also had CCC installed. Pulled card and it was physically fine...fan was working. Uninstalled ALL graphics drivers from my computer and uninstalled all ATI software. Reinstalled card. Installed CCC. I did not install the Overclocking ATI tool. Booted up and never had a problem since. I do pop my cover off when playing graphics intensive games and I don't know the temps it's running, but obviously my overheating issue was solved. I also pulled it off the floor and put the tower on top of my desk. This problem only occurred while running OBLIVION and would play COD2 max specs great.
AMD xp3000+
2gb pc 2700
ATI radeon 9800XT
120GB Maxtor 7500rpm
DVD drive
CDRW drive
aftermarket NIC card
old soundblaster card
one case fan
factory power supply / fan
disabled multicard reader, 3.5" drive, onboard sound, onboard FDC, PS2 port, Parallel Port