The back window fell and will not roll up.
If the rear window has fallen into the door, then it is likely that the window regulator has failed. It is not uncommon for the cables to snap, causing the window to fall down into the door. As accessing the regulator, requires disassembly of the door, I would recommend having a professional technician, such as one from YourMechanic, diagnose your window in order to ensure that is is repaired correctly.
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