Is the lock button light lit? The unit may have been placed into child-safety keylock mode. Try pressing and HOLDING the lock button for approx 5 seconds. It'll beep once when initially pressed, then should beep again with a slightly different tone (the light will turn off).

Next thing if that doesn't work, cut the circuit breaker to the unit and then reset it after about 30 seconds. It's got a microprocessor and they can go a bit insane from unstable power.

What a cool idea to try the child lock, dadoes.