|Do you have the manual? This section refers to AGP cards, but it's worth a shot:|
"the onboard VGA driver can’t be removed completely, and to solve this problem, please follow the steps below,
1. Disable onboard VGA utility under the operating system, and reboot PC. After PC restarts, the system will automatically set the AGP VGA card as the graphics adapter. Or,
2. Re-install your operating system to ensure the AGP VGA card function can be used."
BTW, are you sure the video card works? Have you tried an AGP card in the XGP slot?