Try this, open Control Panel, open System, go to the Advanced tab, click
settings, place a check next to "Let Windows Choose What is Best for My
Computer," click apply and ok.
If that fails to resolve it, try reinstalling the drivers for your graphics
card, still no luck, visit the graphics card manufacturer's website and find
the latest XP compatible drivers for your card and install them according to
their instructions.
Something else I neglected to mention and you might even try this first.
Try using System Restore to take you back to a time prior to when this
began. Start\All Programs\Accessories\System Tools\System Restore.