I think you have a old computer on your hands. Usually with visual glitches such as that it is a graphic card issue, RAM is to full to properly run, and or just a VERY out of date computer.The same thing happened to my friend, her computer was very old and she got a new one and it worked beautifully. But I would try to do some of the anti-virus programs in the mean-time
If you have a Anti-virus program I would run it just in case it isn't a virus.