A microwave that is not turning on or is turning off by itself is usually caused by overheating or a low power supply. It could be that the power is cut off by something like a fuse failure.
Microwave Oven Tripping Breaker What Is Causing This Microwave Oven Microwave Breakers
If your microwave is not working or has stopped working there could be a few reasons why.

Microwave not working but has power. If any of the door switches fails the microwave will not start or heat. To determine if any of the door switches are defective use a multimeter to test each of the switches for continuity. IT WILL MOST DEFINITELY Electricute you.
If the microwave still looks and sounds like its working but its just not heating--that means your magnetron has likely failed. Once youve determined that the GFCI outlet isnt what has caused a lack of power to your microwave one issue might be a blown fuse in the microwave. DO NOT tinker with your microwave oven because they can give you VERY NASTY SHOCK.
Ad Good Price on Chinese Utensils Trusted Audited China Suppliers. For example the issue may be with the fuse door switch or because of burnt fuses. The microwave fuse is a safety apparatus that will stop the flow of the electrical current to the microwave.
Ad Good Price on Chinese Utensils Trusted Audited China Suppliers. If your microwave oven stops working then you should get a professional. If the fuse is blown the microwave will not work.
We will cover the possible solutions one by one to help you fix this annoying microwave issue. A thermal fuse stops electric current flows to your microwave as a safety setting. The magnetron is the part that actually creates the microwave to heat the food and it commonly goes bad and rarely gives a warning.
If the issue with your microwave is that it has power yet it doesnt function properly then it could be due to multiple causes. However if your microwave doesnt heat up at all it could be in Demo mode. The microwave powers on but wont work.
Some things which indicate this is the case include. If the microwave oven has power going to it and it will not work the fuse is the most likely part that has gone bad. When the microwave door closes the door switches actuate in sequence to ensure that the door is closed properly.