DIAGNOSIS Debris (food crumbs, hardened spillage) is lodged in the turntable track or the roller guide assembly is misaligned or broken.
FIX Remove the glass tray and the supporting ring underneath. Wipe the entire cavity floor and the inner/outer tracks with a damp cloth. Inspect the plastic roller guide (the small wheel in the center) for cracks. Reassemble, ensuring the ring's alignment tabs slot into the motor coupler and the glass tray sits flat on the ring.
IF THAT DIDN'T WORK The issue may be the turntable motor itself. Listen for a humming sound without the tray. If the motor hums but doesn't turn, it's seized. If there's no sound, the motor or its connections have failed. Both require a replacement motor part.
HEADS UP Always lift the glass tray straight up to remove it. Dragging it out can misalign or damage the roller guide and track.