The mechanism that opens and closes the window stopped working.
The window regulator or motor is the most likely cause of the window not going down. If you hear the motor running, but the window does not move then the regulator is broken. If you do not hear the motor then the motor may be the cause. If you need assistance with this, I would have a certified mechanic, such as one from YourMechanic, inspect your window and replace your window motor if needed.
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