In a situation where a unit that has been functioning correctly has suddenly stopped functioning for no apparent reason the issue is likely an internal electronics glitch caused by a power surge. To resolve this issue an internal electronics reset is required.
Disconnect the transmitter (base station) from both the audio source and the power source and at the same time remove the batteries from the headset. Leave the system disconnected from power and the batteries out of the headset for 15 minutes. This gives the internal electronics unit a chance to reset back to factory settings.
After the reset period reconnect the system to power and put the batteries back in the headset and test the system.