I'm having the same problem a big hum and it blows the internal fuse. Replaced two fuses.
It could be a bad in-line circit breaker fuse. Unplug the microwave and take the outside cover off. Look for the in-line circuit breaker fuse. Use a plastic fuse puller (not your hands or a metal tool as there is still voltage stored in the microwave even when it is unplugged). Look at the fuse and see if it is blown. (The metal wire running length of tube will be broken. If you have one, test with an Ohmmeter.
locate the microwave's power supply cord.Remove the power supply cord from the wall outlet.Wait one to two minutes.Re-insert the power supply cord into the wall outlet. The microwave is now reset.
Usually answered in minutes!