it goes down but not up or what?
If it comepletly stoped moving (up and down) then it might be the motor driving the window thats gone. Check fuses first though.
If its just started moving REALLY slow, then might also be sign of motor starting to go.
Could also be because of wear to the thingies around the windows.
My windows started running REALLY REALLY SLOW. So i sprayed that edge around the windows with some lubricant, and that helped. So you could try that.