I'd also be checking that all fans in the PC are working correctly. It could be an overheating problem.
Also, the info about the display driver problem could have relevence. Perhaps the display driver is corrupted. Try this:
* download a display driver installation package from
www.nvidia.com I'd suggest you use the 'Archived drivers' there, and download the last of the 4x.xx series drivers. Later driver versions are not really optimal for GeForce 4 cards.
* Right-click My Computer and choose 'Properties' to bring up System Properties. Run Device Manager from the Hardware tab. Locate the entry for the display card and choose Uninstall. Do not reboot.
* Use Add/Remove programs to uninstall any NVidia display driver entries you see there.
* Reboot, and cancel out of any 'Found hardware' dialogues which appear when windows restarts.
* Install the device driver by running the executable file you download from NVidia.
See if that helps.