It's possible you deleted you video card/driver. Doing the system restore Soapets mentions is your best bet. If you don't have XP and the system restore, do you have the CD's that came with the computer? Try just reinstalling your video driver. If you reinstall the entire operating system you will wipe out everything on your computer, so DO NOT do that until you've done a back up and have all your pictures, etc in a safe place OFF the computer somewhere.