I have had 2 flat screens that the sound went out. Threw them both into CG garbage cans. Figuring they are like computers no one fixes them because its cheaper to buy a new one.
3rd flat screen the antenna coupling came loose. THAT one I took to the repair shop and they replaced the board for that. They say they see that a lot.
I asked him about the ones I had that the sound went out. YUP there's a board for that also and right after cable connections loose, sound board comes in second...........on what this TV repair shop call's REALLY CHEAPLY made flat screens. And that his TV repair shop business is really booming once again for just that reason!:B
Soo it sounds like your sound board went out also. Take it in if you really like the TV. My repair costs were well worth it.