Trying to fix a comp, no video signal showing up?

First try working from DOS - get either an MS-DOS disk or an win98se boot disk. If you can boot to this and see the screen then the video card is fine. If so, then wipe the system and start over by reloading the OS. IF you are trying to preserve the hard drive then you need to remove that drive and either place it in another system or in an external enclosure to see what is one it.