Mechanical issues 

1. Manually move the laser head along the X/Y axis across its full range of motion and check for jamming points.  
2. If any, check the tracks, belt, belt pulley, and other mechanical parts for any breakage or deformation. If any, replace them with identical ones.
3. Lubricate the tracks.

Electric issues 

If you have ruled out the possibility of mechanical issues,

1. Swap the plugs on the X and Y drive units.
2. Test again. 
3. If the laser head is moving smoothly along the X-axis and has stopped somewhere along the Y-axis, then the X-axis drive unit is faulty.
4. If the laser head is moving smoothly along the Y-axis and has stopped somewhere, then the Y-axis drive unit is faulty.
5. Replace the faulty drive with a new, identical one.

If swapping the plugs has failed, contact Customer Service.