Firstly go to the Bios, usually you press delete when the computer switches on but it'll probably tell you on the screen. Look for a setting to disable the onboard graphics and make sure it is disabled. Some motherboards do this automatically so if theres nothing in the bios its probably automatic. Then try reinstalling the drivers which you got with the card, if that doesn't work then uninstall the drivers totally and reinstall them from scratch. If that makes no difference try the Nvidia site for updated drivers for your GeForce card and try them. You haven't said which operating system you use, if its XP then download the newest drivers from Nvidia and install them, deleting the old ones first. Its possible that your drivers you got with the card aren't XP compatible.