the same exact thing happened on my s13 a few months ago, the belt wouldnt come back over my shoulder, took it to a pro and they said that if the pass. one works then its not the fuse, so they said to come back the next day to check it out. the next day it was working, prolly just something in the way of the track, i tried clearing the track but nothing was there, it just started back up for no reason next morning, so if pass belt works its not the fuse, maybe the motor is blown?