I have no idea how it happened but, without warning, the open GL stopped working and I tried everything I could to locate the problem. In the version I have on my laptop, in preferences, there is a tab for open GL. In my desktop version, that option disappeared. So... I uninstalled the program, thinking I could download the demo and then use my activation code. Found that I couldn't do that. Then I reinstalled PI from the disc but I guess it is an older version and doesn't work with Windows 7. How can I get the program back???