I had an issue with one that got moved. The shutter assembly is opened by a motor with an offset cam on the right hand side of the machine. There is an outer ring on the cam and it had become lodged in between the the frame and the rest of the cam. The laser assembly comes out pretty easy from the left and then you can reach in and touch or see the cam at the other end. While you have the laser assembly out try moving the shutter by hand. I suppose it could be bound up or something along those lines. I've not had the pleasure but the motor could be bad or the shutter sensor could be failed.
Step aside, noob