Hi and welcome to justanswer.I`m going to help you with your tv but first i will have a few questions;
Is this tv connected to a cable box/converter,satellite receiver,digital converter etc ?Do you have other equipment like a dvd,bluray,games etc. connected to this tv ?If so, do they have sound ?
yes it's conected to a cable box.
O.k then there is a very good possibility that your cable box was upgraded online and needs to be re-booted.Disconnect the cable box`s power cord(cable box only) for a couple of minutes .In the mean time turn off the tv and turn it back on only after you plug back the cable box`s power cord.Note that you may have to give it a couple of minutes to reboot after you plug it back, just give it time.
Glad to hear that , enjoy.
Thank you for the "excellent service" rating.