Like jsc said, "no video" problems can be caused by any number of things. It most likely has nothing to do with your video card. Please perform ALL the steps in the checklist linked above and let us know how it goes. I'm guessing a stick of RAM may have failed. Try booting with each stick of RAM by itself (step #6 on the checklist).
You also need to tell us a little more about what exactly is happening. Do the fans spin? Can you hear the hard drives working? It's hard to help without having a clue what hardware we're working with. Is this an OEM system like Dell, HP, etc..., or is it a system that you or someone else made?