Senheiser lavalier issue

I have been using the Sen. Lavalier mics for about 8 years. Today setup my system for church, found there was a signal being transmitted to our board, sound came out of the headphones, nothing from the mains. Db level was set at 30, tried 20 and 10, changed frequencies, nothing happened, still could only hear through headphones! Our handheld mic on its own channel was working just fine, plugged my lavalier into that channel, changed frequency, still the same, only through headphones! Stumped, prayer didn't work either!!! any ideas???