Nissan Maxima windows

I have a 1995 Nissan Maxima with 190,000 miles. All of a sudden my drivers side window just start sliding down. I can hear the motor working but it will not raise or lower the window. I can manually pull the window up but when I start driving it just starts sliding down. Today the back passenger windows started doing the same thing. I don't ever raise or lower the back window and as I was driving it start sliding down. I live on a gravel road and I was wondering if maybe the windows have gotten knocked of the track.