The start button stopped working without warning. All functions that do not require cooking work, clock, timer, fan and light. Any function that requires the microwave to work only count the time down, there is not movement of turn table or sound of motor, I hear a distinct click when I touch the start button as though it is not engaging however defrost etc do not work either without the sound. We have unplugged and plugged back in but nothing changed. Can you offer any suggestion?