All LEDs are lit but even after battery change - no sound

After plugging in the base, connecting the audio source and turning on the headset I hear no sound. All LEDs light up as normal.

I have tried the following :

1) I have tried to change the channel (tune button) - the first time I heard the beep but still no audio and now the headset no longer beeps

2) I have changed the batteries on my headset

3) I have tried different audio sources

4) I have tried different plug sockets

Is the transmitter or reciever dead ?

How can I really find out what's wrong ?

Has anyone had this problem before or have a solution please ?