There are two reasons why your wiper may have stopped if the motor is still running, one of the nuts may have slackened on the drive linkage or the nylon gear in the drivehead is slipping/stripped. Either way the complete motor/drivehead unit has to come out to allow repair,in the first case it is just a matter of resyncronising the linkage and tightening the nut, the second is more complex.
This link shows the procedure for removal;http://members.lycos.nl/mbenz/windshield_wiper.htm.
PM me if you need any more help.
Geo.