Trolley not rotate.
The reason may be:
1) Hook''''s friction-gear loosens.
2) Motor is not work.
3) Trolley is not in position or tray's size is out of range.
You can do:
1) Screw locks screw of friction-gear plate.
2) Check whether motor cord is loose or motor is burnt.
3) Place trolley in position and tray in proper states.