After an upgrade of XP, you may notice the Display Adapter category missing from Device Manager completely. Scans by Add/Remove Hardware find no video cards, and the install program for your video card complains that it either can’t find a compatible card or that your existing “standard” driver has a problem.
Cause: Chipset drivers were screwed up by the upgrade.
Solution: Re-install chipset drivers. In my case, the latest VIA 4 in 1 driver from my motherboard manufacturer’s website.