Warranty on microwave oven just run out?
Your food is just as cold as before inserting for heating.
Microwave looks like it worked normally, the timer counts down to the end of the heating process, the plate turns as normal.
But food is still cold.
Most common fault is small glass fuse has burned.
How to replace that fuse?
Taking apart microwave can be very dangerous if you do it improperly...
There is a high voltage capacitor in there that can be still charge and can give out a lethal shock.
This fuse is placed next to the transformer in the white tube.
Before you do anything in faulty appliance make sure is disconnected from mains.
The capacitor may hold electricity, need to be discharged before performing any repair.
You can wait for least 30 minutes to discharge capacitor itself or using insulated pliers connect 2 capacitor connectors.
You may get a loud "SNAP" (which is unlikely) and that indicate the capacitor is discharged, do this a few more time to really make sure the capacitor is discharged.
Open the tube using a screwdriver, replace the fuse with a new fuse.
Close the tube and place in designed area.
Before close, the microwave oven case makes sure that high voltage wires are away from fan blades.
Close the microwave oven case, make sure no gaps left.
About 15 minutes of work and your appliance back to life.