Installing the latest drivers will not screw up your video card so long as you install the correct one... It will make it better.
Since you say you haven't done anything to your cards, this is probably the problem.
Find out what your card is, go to the manufacturer's website, and download the drivers for your card.
EDIT - Do you have Windows XP? If you do, and you are afriad about messing something up, create a Restore Point before you install the driver. That way if something does go wrong, you can revert to the way it was before it happened.