I installed a Dell-version GeForce 6800 into a Lenovo desktop computer's PCI-E slot, and upon installing the drivers (81.98 forceware - official drivers from NVIDIA), it no longer shuts down properly. When I choose shut down from the start menu, one of three things will randomly happen:

1 - it crashes and reboots (I know it crashes because it then runs ScanDisk)
2 - it goes to a screen that says "It is Now Safe to turn off your computer"
3 - it goes to a screen that says "Press any key to continue..." and some time after pressing a key (probably 20 seconds or so) it does #2 above.

I've tried disabling all NVidia-related stuff in the MSCONFIG from running on start up but still the problem exists.

Interestingly enough, the RESTART option works fine - it will go to the "Windows is shutting down" screen and then re-boot.

Any suggestions or ideas? My searching hasn't found anybody else with this particular problem. Note that shutdown worked fine when I had an ATI graphics card installed.