Very strange, all the keys from "E+" down to the "+" sign do not work. Every other key works. This calculator has been with me since I started highschool in 1986 so I'd like to repair it if possible? Any ideas? Many thanks.
Try pressing down on the faceplate (firmly but not so hard as to dent it or break the plastic) below the LCD but above the keys, and see if that makes the offending keys work again. If it does, you need to disassemble the calculator, and add some extra padding behind the keyboard contacts. Refer to the excellent instructions here on how to open the unit, and what you need to do to make the keys work again: http://www.hpmuseum.org/guest/brogpion.htm