Every time I start up a game it either crashes, or is too glitchy to be playable. I don't know if it is a problem with my graphics card or what, The Computer works fine for normal stuff like surfing the web, I can't play any game I have except assassins creed 3, but when I play that game there is a visual glitch that renders the game unplayable. I just built this PC, I don't know what to do, Help?