Never ever had a problem with any window motor or switch on my GM's. For me and others I know it has been a broken wire inside the rubber boot between the door and the body, wires travel from the body to the door and after opening and closing the door a million times the wires work harden and break.
With the key on try holding the window switch in the direction you want it to go and open/close the door, sometimes if the wire is holding on by a strand you might get some movement out of the window for a split second, its worth a try.
