I've had problems with lots of lines..green ones etc and simply changing my resolution did the trick. Look up your graphis card as well and download the latest drivers for it. If its onboard graphics (hope not since you are playing games) just look up the people who made the computer eg. Dell or HP.
If its a card in a pci slot then of course go to the makers of the card for the drivers eg. Nvidia
If all that fails then go next door and borrow your friend's display and plug it into your computer and see what happens. If its a laptop then you are out of luck but there should be a port for an external display somewhere on your laptop. Another option would be to do a system restore to a point where your machine was working fine.
Best of Luck.