more than likely what has happened is that the window has come unglued from 1 of the 2 places that it is attached to the regulator. it is a complete PITA. if thats whats happened you'll have to remove your door panel, remove the window, and remove the regulator from the door. take a "whiz wheel" as i call it, and remove all the old glue from the regulator mounts and the small areas on the window. then get either some clear rtv or whatever glue/epoxy ford recommends, use that, and roll the window all the way up as high as it will go and let it sit overnight.
after the window has set, spray some silicone lubricant on the rubber window runs so that the window doesnt get stuck as it slides up and down. i had to reglue my window 3 times before i figured out why the window kept coming off the regulator.
this is a common problem on 99-00 stangs.
i wish the window was bolted to the regulator like hyundai's and toyota's...then this wouldnt happen.
also, if you dont want to remove the window completely from the car, you can use a "window wedge" which is basically a rubber wedge. once the window is detached completely from the regulator, pull the window up all the way and stick the wedge between the top of the doorframe and the window; and the window wedge will hold the window up and out of your way.
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/ Flat Rate Hyundai Technician

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