My phone is 'Muted' and calls are not possible!?

Hello, I have a Binatone Cordless Phone....Symphony 3325 Model. All it's functions seem to be working alright except that it suddenly got 'Muted". It does not make a dialing tone when calling a number & the call is not possible. When I try I press the 'Return' button while dialing the window displays 'Muted"! It does not receives calls either, although other function buttons seem normal!
Appreciate all the help I can get. Thank you and good day.