I have a thermador built-in microwave (model MBBS) that's around 2 years old and suddenly died. There is power to the unit; the display functions normally. When the "start" button is pressed, the display timer counts down as if the oven is working, however there is no cooking going on, and no fan sound or any other sound which would signify normal operation, nor does the turntable turn. What is (are) the likely cause(s)?