Most likely it is the Video Card. If it is integrated into the motherboard, you would need to purchase a new card and disable the on-board video. (sometimes that is automatic, sometimes you need to enter the BIOS)
If you already are using a Video Card, try reseating the board and see if that helps. I have had computers that appear to be dead and have only needed the memory sticks (RAM) or PCI cards reseated.
Edited by rigacci, 23 December 2008 - 01:18 PM.