Win XP–double click opens properties

Hi, all! I am having issue with my laptop. It’s a Dell Inspiron 8100; Basically, it is acting as though the Alt key is being pressed. Double-clicking on desktop icons opens the Properties menu. I can right-click and choose Open, but I can’t type anything because, again, it is acting as though the Alt key is being pressed, i.e., typing F brings up the File menu. I can log on as this user, and for the first while there is no problem, but then suddenly it will start happening. If I log in as a different user, I still have the same problem. I have scanned my computer with Ad-Aware SE and deleted any viruses found. Also, I checked the Device Manager, but didn’t see any ATI anything. Any help is greatly appreciated. Thanks!!!