To resolve this kind of problem:

  • Check that the switch contact is closing correctly when pressed: use a multimeter to buzz out the cable to the ribbon cable header.
  • Check that no other pushbuttons are stuck down: the board will not respond if there appear to be more than 1 pushbuttons pressed.
  • Check there is no wiring "short" that has the effect of making two switches appear to be pressed. This can happen from loose strands of wire at the end of unused parts of the ribbon cable.