How to change my OpenGL settings

When I want to start the game Medal of Honor I get the following message:
"OpenGL vendor string is NULL". The game have been starting properly before, but my motherboard was replaced and now I get this. Could someone please tell me where I can change my OpenGL settings? or even better, how to resolve the problem?
please!!!!!!

Forgot:

- Got windows XP Professional
- Videocard: Nvidia G-force 4 Ti4200
- Have downloaded the latest drivers for openGL from Nvidia.com
- AMD 2000+ procesor (1.7 Ghz)
- DirectX 8.1b