Maybe it's a faulty connection with your graphics card. What is the resolution right now? It should be at least 1920x1080 if your PC is at the best specs in the market (which would probably be an i7-2600k, 16-24Gigs of RAM, Dual SLI GeForce GTX 580s, a 7200RPM with at least 1TB of space, a PSU with at least 700W---if you don't have these... well then... I don't think it's the best.)
Try adjusting your resolution all the way to the largest numbers.
Also, how is your monitor connected to your card? HDMI, DVI, VGA?
As a last resort, open up your system, disconnect the graphics card(s), clean the motherboard and cards, reinstall the card(s).