Warning:
Microwave ovens contain very high voltages which can remain fora time even when unplugged. We will not attempt a repair and we do not recommend that you try.
Possible cause:
Blown fuse.
Remedy:
Replace the fuse with a new one of the same rating. If the oven works then fine. If the new fuse blows (you might hear it) or the oven still doesn’t work then buy a replacement microwave.