CompuServe Messages

I can't seem to get out of the SHOW command on the project menu. I did the first example of the tutorial with no problem but when I tried to look at a renderd cell it would load up and show it but I can't get out of the SHOW screen and when I use the front/back gadget and go back and click on the Project window my mouse vanishes!!. I have tired to klick on the screen and everything but it will not go away and I have to reboot to get back into imagine.. HELP!!!