what used to happen to me, my video card didnt like the newest driver for some reason. so i ran an older one and never updated.
http://www.oldapps.com/old_version_nVidia.php
download one that was from before, but has functionality with your card.
and take it out and clean the connections with a pencil eraser. blow any dirt off. and reconnect it.
if that doesnt work. im pretty sure your video card is crapping out. dont reformat yet! unless you have everything backed up. then order is arbitrary.