Go Here » http://www.ptc.com/support/index.htm?dd=Support

Click on the self-help section or try the update advisor, you don't have to register a product just give them some basic details (so even if the school is handing out dodgy copies, it doesn't matter). If your getting artifacts on screen it might be an issue with the OpenGL driver it's using for the overlay, but you should be able to find a solution on there site.