There are any number of reasons for this does it sound like the motor is still running but not lifting or lowering the window or is there no noise at all if there is no motor noise it will be the motor however if the motor sounds like it is still running it will be a problem with the lifting mechanism which is basically 2 metal runners with a network of cable to lift and lower the window and the glass itself is held up on plastic blocks with 2 round clips in the glass if it is this the mechanism starts from 50 quid depending on dealerships
Aaron
April 2009