Yep. First thing to do is uninstall your drivers, completely. Dont leave even a trace of them. If you installed the latest drivers off the Nvidia website, I'd even run a registry cleaner to get all references to the driver out of your system. Download this one.
http://www.nvidia.com/object/winxp_2k_61.77.htmlYou'll need this older driver, the new ones dont work so well with the old Nvidia cards. The MX 4000 is 2 generations old now. It will do ok, but dont push it too hard. If you have to keep it for awhile, I'd consider buying a fan/heatsink combo and installing it.
Reboot your computer. When it detects the video card, and asks for drivers, cancel out of the setup. Install your drivers and let everything find its home. Reboot.
Reinstall Direct X 9, in case some of the files got messed up or point to the wrong places. Just a precaution. Reboot.
Test.
If you weren't having the lockups before, I'll assume everything else in the system is kosher, but bad drivers on just about any piece of hardware could cause the problem.
