I have same element 408 and i cannot get the mite off to get my sound back i have an antenna boc for my cable

[henrylaura913]

I cannot get my volume back on tv it is stuck on mute and already changed batteries

 

[Alabalcho]

Does your TV has physical buttons for channels / volume?
Turn on your phone's camera, and point the remote . Do you see the remote LED when you change volume? Does your remote support multiple devices?