Hi
Its possible that the drivers havent been loaded correctly for the video card you now have installed in your PC, here's an idea
go into device manager and remove any reference to the video card/s reboot and windows will try to reinstall any video cards it finds it may pop up a box asking for the driver for any card it doesnt have the drivers for.
Pop in your driver CD and point windows to it, check in device manager to make sure it is now showing correctly.
Lastly make sure you have the latest version of direct X installed as well.
Regards