Sunroof motor activates, sunroof doesn’t

A few days ago I was in my 09 mini cooper s convertible and tried to put the top down. It has a 2 step toggle over the rearview mirror, anyway it moved a few inches and stopped ,then made a grinding noise. I released the switch and tried to re-close it, it went forward slightly but stopped short of sealing with the grinding again. I did try it a few times, now the motor starts and sounds normal but nothing moves. The cover to the motor was missing when I bought it and I can see the main sprocket turning but that it. Is there anything I can try?
I would appreciate any help.