well, you can start by telling me what kind of video card you have, and i could just redirect you to the proper drivers page.
if you don't know what video card you have, i'd say to look in the devices manager, but if the drivers aren't installed, there's not really a point...
try to look around what came with your computer for any relevant info about it.
if that can help, to access devices manager, just right click on "My computer" select properties, click on the hardware tab and click on device manager.
check under display adapter for your video card.