What should I do if the hook of the sewing machine does not turn?

1. If it is a computerized sewing machine; it should be that there is dust in the internal sensor of the front pulley of the sewing machine. The solution is to loosen the pulley and take it out and do some sanitation inside the sensor and pulley.
2. If it is an ordinary sewing machine with a motor, it should be that the belt pulley fixing screw of the sewing machine of the machine head is slipping. Another possibility is that the machine is stuck. Check whether the hook is stuck on the thread and do the cleaning work!
3. If neither of the above two methods work, the bearings on both sides of the shaft are broken.