Hello. I had the exact same problem, and it was solved following the procedure on this page : https://en-us.sennheiser.com/what-do-i-do-if-my-rs-120-unit-suddenly-stopped-working
In short :
* disconnect both power and audio from the base, remove the batteries from the headgear ;
* let it sit like that for 15 minutes, enough time for the electronics to relax ;
* then plug the power back in the base, put the batteries back in the headgear, check whether the red "charge" light goes on, and finally plug the audio back in the base.