The PanelView Standard's bezel parts are glued together pretty tightly to get the NEMA 4X environmental rating, so the keypads aren't field-replaceable. You might be able to get the terminal repaired by Rockwell, though.
Error code 31 on PV terminals is exactly what it says; the autotest procedure found one or more of the keys on the keypad were turned on at startup. You can simulate it just by holding a key down during bootup of the terminal.