A relative has a wall mounted CHAMBERLAIN 880LM "that hasn't worked in years." The unit has power but only displays "PRESS THE PUSH BAR TO ACTIVATE CONTROL SEE USER MANUAL". None of the buttons are responsive. Detaching the wires (removing power) and reattaching them does not resolve the issue. The garage door opener is a CHAMBERLAIN 45DCBR5 Any help is appreciated and thank you in advance.