It depends on what he updated. It sounds like your video driver has been removed and XP is using a generic driver, but it could just be messed up settings. To see, try this:
Right click on an empty location on your desktop and choose Properties. Now click on the Settings tab. Make sure the color quality is set to Medium (16 bit) or Highest (24 or 32 bit). Then move the Screen Resolution bar all the way to the right. Hit the Apply button and hope for the best!