Sounds like windows driver issues. I am assuming it worked prior to the new video card.

1. Put the old vid card back in.
2. Download the newest drivers for your new video card.
3. Switch to the windows default video driver. (max rez should be 1024 if you are using winxp)
4. Shutdown and put the new vid card in.
5. Boot up and update the video card drivers using the downloaded file and not the file on the disk the Vid card came with.

Let us know what happens.