If the keypad doesn't respond, the reason is often the grounding screw on the back of the keypad. If this is screwed in too tightly, the keypad can get blocked and won't register inputs anymore.
On the back of the keypad, there's a tightly screwed nut in the middle. Loosen it a bit (make it less tight).
After that, test the keypad. Most of the time, the problem is that the nut is screwed on too tight, and that's what blocks the keypad.
