Ok, try this: (for XP, probably the same on 2kpro)
Hit the windows key plus the pause key to bring up the system properties window.
Click on the hardware tab
Click the device manager window
Click on the display adapters plus sign, then highlight the subtitled video device (nvidia or ATI, whatever)
Right click on that device, highlight and click properties
Should say "deivice is working properly. or "no installed drivers for this device, etc.
Click the driver tab to update or roll back to a new driver, or walk through the troubleshoot tab.
If that don't work, install and run
http://www.belarc.com/free_download.html
this will tell you the mobo, processor, and video device installed. The Video device makers webstie would be the next stop for trouble shooting.