If you system is generating a code 12 and running at 800x600, onboard video is disabled, and another AGP card works fine in the system. Go to the view option in windows device manager and select resouces by connection. Expand the IRQ and memory sections. Look for any conflicting or shared resources. If you are showing that a device called VGA save legacy is being shared, try turning down the AGP aperture.

For more information on AGP aperture see the FAQ listed here: https://www.evga.com/support/faq/?f=59067