DIAGNOSIS The drive coupling or motor is obstructed or failed. First, check the physical assembly.
FIX Remove the glass tray and the plastic roller guide underneath. Check that the drive coupling (the three-pronged plastic piece on the floor) is not broken and is seated on the motor shaft. Ensure the roller guide and tray are aligned correctly. Reassemble and test.
IF THAT DIDN'T WORK The turntable motor may have failed. Listen for a faint hum when the microwave runs. No sound indicates a dead motor. This part (part # AP4353289) requires disassembly to replace.
HEADS UP Always ensure the glass tray and roller guide are installed correctly before operation. A misaligned tray can jam and break the drive coupling.