check your video card

Plug out and plug in your video card may be working...

Also, you may insert another video card in your computer, or you can insert your own video card in another computer to see what happens...

Also...if you can still start your computer with a MS-DOS boot disk and see MS-Dos command prompt, it probably means your video card is ok, but ur Windows system may have problem to affect the video card's working. If so...reinstall your windows system