Hi @mnkquqlvamire0y
If it works when the USB cable is connected but doesn't work when the USB cable is disconnected, it sounds like there's a problem with the battery in the headphones.
Either it is not being charged when the USB cable is connected or it has failed.
If you have a DMM (digital multimeter) you can disconnect the USB cable and then open the headphones and check what the voltage on the battery is.
Here's the ifixit [guide|146892] guide, that will help.
Unplug the battery from the board and then measure the voltage between the red and black wires on the ''battery cable plug''. It should be approx. 3.7V DC if the battery is fully charged.
If it is a lot less than this consider replacing the battery and check if it charges OK and if the headphones work without a USB cable connected.
Search for ''533-000132 battery'' to find suppliers that suit you best.