Okay, lets progress further on this.
I assume that you have DirectX installed.
If not, that might be part of the problem.
Start by running dxdiag
You should be able to run it from the run box on the start menu.
If you need to find it, it should be in Program Files\DirectX\Setup
Run all the video tests.
If the system hangs or fails any of the tests, that is your clue as to what's wrong.
There are at least 2 other members having 3d acceleration problems. The suspect in both cases is a combination of registry and file corruption.
At the moment, they are both considering formating their drives and starting over.
If you had a different video card in the system prior to the Nvidia card, you may have some driver files and registry calls that are attempting to access and load files for the old card.
While it isn't fun, I have corrected this kind of problem in the past by searching through both the registry, and the system files to delete all traces of an old video card in order to get a new card to function properly.
It can be quicker to start over!
Chas