Originally Posted by
lynx
Looks to me as if the bearing on the video card heatsink fan has failed.
If that's the case the video card will be overheating, but should shut itself down before any serious damage occurs. The very fact that you say it hangs after 20 minutes in safe mode seems to bear that out.
The question is, what made it fail in such a dramatic way, and has the same thing or the failure itself damaged any other parts. My guess would be that if there is any other cause it's going to be the power supply. Difficult to check out, especially if it is just a failed capacitor that's causing excessive ripple on one of the 12v rails. If it is a cheap PSU you should probably just replace it.
As for the 9800 card, you need to get a replacement fan (not very likely) or a complete aftermarket cooler for the card.
Just out of curiosity, why did you re-install XP after removing the 9800 and adding the 7500. The drivers for the 9800 would have happily worked with the 7500 AFAIK. Now you have the extra problem of trying to re-install XP.