my advice is to try your screen and/or computer with another screen and/or computer just to narrow down the possibilities. or first you could check the drivers to see if that item is working correctly. you may need to update the drivers if you tryed to boot your computer from a disk. you might need to put in the drivers disk. but im guessing that its either the video card or the screen.
the same thing happened to me and i think it is the video card. I opened up my pc and i can't find, it is not visible. Can you tell me what it looks like?