In my TOSHIBA 36ZP18P, L and R speakers suddenly stop to work. The volume sliders in the sound menu also disappeared. Other speakers (sub and rear) continue to work normally. There is no sound neither I use ext. speakers neither I use int. speakers. I try all possibilities in menu and with the switch ext/int and nothing happened. What is wrong with my TV? How can I activate again L and R speakers? Hope I was clear enough. Thanks for any help.