IS IT MANUAL WINDOWS , CHANCES ARE THE GLASS HAS PULLED OUT OF THE MECHANISM , TAKE OFF DOOR TRIM TO SEE . YOU MAY GET AWAY WITH STRIPPING IT OUT & REASEMBLING BUT LUBRICATE THE WINDOW RUNNERS WITH WD 40 OR FAIRY LIQUID SO THAT IT ALL OPERATES EASILY & DOESNT PULL ITSELF APART AGAIN
PHIL G, April 2009