Do you get any beeps during the power-up tests? If not, the BIOS can see the video card. In that case, the video cable might be faulty (or the connectors have become corroded). Do you have another video cable that you can try?
If you are getting beeps, the length and number (e.g. one long followed by three short) may give more information, although motherboard manufacturers don't alway use the same codes.
Happiness in intelligent people is the rarest thing I know.--Ernest Hemingway