Chances are the keypad (membrane switch) is shorting, or the control panel as an assembly may need repair.
If you or someone you know decide to work on it, we have *critical* safety, disassembly, and troubleshooting info at our site, and our link is at our listing here on FixYa: http://tinyurl.com/yzjozk
You can usually find helpful exploded view diagrams and order parts by entering your full model number here: http://tinyurl.com/gv383
There should also be a "mini-manual" hidden inside the unit behind the control panel, which is very helpful when troubleshooting. It shows you how to test the keypad.
Also, we repair these for $39.95 (in most cases) for customers nationwide via mail. If yours needs a keypad, we could also give you the estimated total repair cost if you contact us with your exact model number.We're happy to help and we appreciate your thoughtful rating of our answer.