If the turntable on your microwave does not rotate, or you can hear a grinding noise, the problem may be with the motor. The motor is typically located below the floor of the oven, and is accessed through the bottom. The motor is normally held in place with a retaining screw and will have two wires attached to it as well. If the motor is making a grinding noise it will need to be replaced. If the motor does not turn, you can check for voltage or continuity with a multi-meter. Make sure the power is disconnected from your microwave before beginning this repair.