Fixing your microwave oven at home when it stops working is a thrifty way of saving money on repair visits. You might find the problem is caused by the power supply, the internal computer or the way food is loaded into the microwave oven. The best way of fixing a broken microwave with no specific symptoms is to rule out common problems one by one. You won't need special knowledge of microwave ovens to fix your appliance.
Verify that the power supply is configured correctly. Test the microwave's electrical outlet with another appliance -- replace the circuit's fuse or reset its breaker to restore power to the outlet. Ensure the power cord is fully inserted into the electrical outlet and, if necessary, the outlet is switched on. A loose connection at the outlet will cut power to the microwave.
Heat a cup of room-temperature water on high for two minutes inside the oven. The water should be piping hot when the microwave chimes -- be careful handling it. If the water is still at room temperature, the magnetron may be defective. Call the manufacturer to arrange for repair.
Open the oven and check that the turntable and carousel are still in place. The carousel should sit in the depression at the bottom of the microwave with the hub connected to the driveshaft. The turntable sits on top of the carousel, divot side down, with the wheels of the carousel inside the groove on the underside of the plate. A loose carousel or turntable will stop food turning and produce uneven cooking results.
Ensure the door closes properly when food is inside the oven. Large plates or large cooking containers may hold the door slightly open even if it appears to be latched closed. Microwave ovens won't start until the oven door is completely closed. Try heating your food on another plate or in another cooking container.
Clear the current program by hitting the "Cancel" button a few times. You might have entered incorrect or incomplete information into the computer and caused an error. Unplug the microwave and wait for at least a minute before reconnecting the power supply. Disconnecting the power resets the CPU after a power surge or other error.
Ensure "Demo" and "Lockout" modes are both inactive. Some microwaves prevent kids from accidentally starting the oven by locking the control panel. Lockout mode is usually canceled by holding the "Lock" or padlock icon button for a few seconds. Demo mode displays the oven's features while it is in the store without ever heating up. Check your instruction manual for exact information about canceling "Demo" and "Lockout" modes.