My Maytag over the range microwave is only 3 years old. No power. Changed the fuse - made sure the outlet worked on other appliances.

Door switch or thermostat or fuse or door switch... did I say door switch?

1) Plug the microwave into the outlet if the microwave won't power up. Make sure the plugs on the microwave match the type of outlet. A four-pronged outlet can only be used with a four-pronged plug. Same with three-pronged outlets---they only work with three-pronged plugs.
2) Inspect the plug. Make sure it hasn't been cut or tampered with. Four-pronged plugs can't be cut down to fit a three-pronged outlet. Three-pronged plugs mustn't be forced into four-pronged outlets. A three-pronged plug mustn't be used in a two-pronged outlet, either.
3) Replace blown fuses, or if there's a circuit breaker, check it for tripped breakers. Sometimes the trip won't be obvious, so cycle the circuit breakers. Turn them all the way off and then back on again.
4) Plug another appliance in the outlet. You will find this easier with three-pronged appliances. Simply plug a toaster, or other appliance into the microwave's outlet, and see if it works. If it works, you know the problem is with the microwave, not the power circuit. Have the microwave serviced or replace it. If the toaster or other appliance doesn't turn on, you know the problem is with the circuit.

Dead appliance, power on wall outlet.

YOUR SAFETY IS PARAMOUNT!

Attempt this only if you are competent.

If your appliance has absolutely no functions at all, remove it from the mains supply, remove the case and see where the mains lead goes in to the appliance and follow the cable until you find the main fuse.
ONLY USE THE SAME TYPE AND RATING OF FUSE TO REPLACE IT.
The usual cause of this fuse failure is the door switches are contaminated or sticking. Check the door switches before putting power back on to the appliance.
Hope this helps.

Dead appliance, power on wall outlet.

YOUR SAFETY IS PARAMOUNT!

Attempt this only if you are competent.

If your appliance has absolutely no functions at all, remove it from the mains supply, remove the case and see where the mains lead goes in to the appliance and follow the cable until you find the main fuse.
ONLY USE THE SAME TYPE AND RATING OF FUSE TO REPLACE IT.
The usual cause of this fuse failure is the door switches are contaminated or sticking. Check the door switches before putting power back on to the appliance.
Hope this helps.

Depending on the model you may need a 15 or even up to a 20 amp circuit to operate the microwave. Check the installation instructions to be sure. What is most likely happening is the circuit in your home is not powerful enough to run the load of the microwave oven. If this is the case it could be dangerous. I would strongly recommend you have an expert examine the house wiring prior to starting the unit again.

blown fuse take outer casing off and replace the blown fuse.
You can use a piece of tin foil around the fuse until you are able to replace the fuse.

problem is a blow fuse inside the microwave, you need to call a appliance repair tech

First, there is an outlet. Plug in something else. Inside the key panel, there are fuses and a thermo sensor. Either may be bad. The thermosensor is about the diameter of a dime, black and 3/8 inch thick...attached to the wall of the chamber. All should have continuity.

It could easily be a bad line fuse and/or line filter. To access you will need to unplug the unit and remove the outside case. Inside the unit, where the A/C power cord comes in, there should be a small circuit card (part #237068) located somewhere with a fuse mounted on it. This is your input line filter board with line fuse. Replace the fuse, first and see if this fixes your problem. This is a 20amp appliance fuse that you can purchase at any hardware store. Make sure you place the cover back on the unit BEFORE you plug it in. It is not safe to have this area of the microwave exposed with power applied. High potentials in the 4,000 volt range are present! If the fuse does not correct your problem, the circuit card runs about $26.00. Good luck and hope this fixes your problem.