Power goes off!
I have the same model as you.
Plug in the transmitting unit into a good working power outlet. Make sure you have the audio connected to a loud source. Turn on the source device producing the loud audio to be transmitted to your headphones. Now see if the transmitting unit's LED light is on. Check headphones for audio. (May have to tune in the headphones and adjust its volume as well).
I recommend that the source of your audio have its built-in speakers off, while still providing audio out to your transmitting unit, via an external audio output. Check your source manual or look for audio jacks on the front or back. There may be a setting to turn this on and for the main built-in speakers to be turned off as well.
If this does not work, unplug the transmitting unit, and then plug it back in again, after waiting for about 10 seconds - all while audio is being provided to the unit. It should come on.
Remember that if the audio to the transmitting unit is quiet OR off for about one minute, the transmitting unit will turn off and you will hear FM noise, loudly, on your headphones. This is due to the "lack of audio" timer built-in to the transmitting unit.