The window may just be out of it's track. It seems to happen to my passenger side door on my mark every couple of years. If you can "help" it down by pushing it down by hand the motor will pull it the rest of the way. Then you know that the motor is ok (I assume you have ruled out the switch). Make sure it isn't going to rain right away in case the glass jams and you can not get it all the way back up until you fix it. It shouldn't take alot of pressure to get the window to move. Once mine is down a few inches, I let go of the switch and see if I can pull the window back up, when only the back of the glass moves up I know I have a mechanical problem with it.