I'm guessing that you're playing the PC version of this game. The PC version can have some problems regarding GeForce graphics cards (I should know since I use a GeForce myself and experienced these problems). Eidos Support still hosts a series of patches for the game. There's a link to the GeForce specific patch on the site, as well as other troubleshooting links. If all else fails then go into the configuration and set the game to run in Software Renderer (Video tab). It's quite an old game so can get by quite easily on Software Rendering without problems.