If the Panasonic NN model microwave does not heat, a very likely cause is that the diode has burned out. Usually visual inspection reveals whether this is the case. If visual inspection does not reveal burnout, check the component with a volt-Ohm meter capable of testing diodes.
Follow proper safety precautions before testing any electric appliance, according to manufacturer's instructions. If the microwave is not working at all, a likely cause is a blown line fuse. It is possible to replace the fuse, but the underlying cause of the problem should be investigated and resolved so it does not continue to occur.
If the microwave runs for a few seconds and stops, its thermostat may be defective. If the turntable does not turn, a likely cause is that the turntable motor has burned out. This component is easy to replace.
If the microwave door does not open, the door spring is a possible culprit. The door spring is located inside the door and should be checked for breakage. The door hook, which normally releases when the door is opened, should also be inspected to see whether it is releasing properly. If the door hook is broken, it needs to be replaced rather than repaired.
If the microwave's exhaust fan is not working, it is possible that the thermostat is defective and needs to be replaced.