You need to be brave, but it is pretty simlple. Basically you are going to clean the rubber keypad and circuit board contacts. These contacts develop a film over time that needs to be removed. That is the main reason telephone and remote control keypads fail over time.
1. Remove the battery.
2. Remove 5 screws holding the bady together and separate the backplate from the main body.
3. Now carefully lift the circuit board out of the main body. Do not disconnect anything, but be careful with the rubber seal that fits between the back and front plates.
4. With the circuit board laying flat on your work surface, remove the rubber keypad. It is held in place over the joystick. Carefully lift it off the joystick and set it aside.
5. Use a clean pencil eraser and lightly rub the contacts on the circuit board. Do the same thing on the keypad by pushing the little knobs out where you can rub them. Blow away the dust.
6. Use a Q-tip with some alcohol to clean the contacts on the curcuit board and on the keypad.
7. When the alcohol is dry, put everything back together in the opposite order.
This should be good enough, but if it does not solve the issue, then buy a rubber keypad repair kit (an example is at http://www.mgchemicals.com/downloads/appguide/appguide0206.pdf
) and try again.