Verify that the roller guide and glass plate, collectively known as the turntable, are correctly positioned on the floor of the microwave. The roller guide sits over the drive shaft of the motor with its wheels in a groove on the oven floor. The glass plate sits smooth-side up on top of the roller guide. Knocking the turntable out of position is easy when loading or unloading food.
The plate used to cook your food should fit within the confines of the turntable so it can turn without touching the sides. The turntable might jam or turn beneath the plate if it is too large for the oven. Move your food to another container, and try the microwave again.
The oven won't accept any cooking instructions or start heating while the child lock is running. Hold the "Stop/Clear" button for three seconds to cancel the lock. Holding the button for a further three seconds reactivates the child lock. This feature prevents children from playing with the oven.
The door must be completely closed before attempting to start the oven. The cooking plate could be pushing against the inside of the door, keeping it slightly ajar, or the door may simply not have engaged properly when closed. Push the door until it clicks and try again.