+1Maybe elec. conn. or motor corroded. If accessible, might unplug and plug a few times and spray both ends with some elec. contact cleaner and follow up with dielectric grease. Also, i would spray window tracks with silicone lube spray.
The taking the motor out, and lubing up the track helped the window move up and down. Try taking out the motor, keep it plugged in and test to see if it moves not connected to the window. Be sure not to lose the nuts that you take off!