And should be listed in the M'Board Makers Manual.
If this is an Off the shelf System then you'll need to look in the Users Manual and if you no longer have the Manual you'll need to look on the System Makers/M'Board Makers Web Site for your User Manual to find out what the Error Message is.
Though if this is a Desktop with a AGP Video Card the most likely thing is that the Video Card has moved in it's socket and is no longer in the proper location to work. Just opening the case and pressing down on the Video Card quite often cures the problem but you may need to remove the Video Card and reinsert it into the socket to make it work again. ;)
Col