I have a sony bravia KDL-40bx450. Although I bought it in May, it has less than 20 hours viewing time on it. I turned it on the other day. The picture is fine but there is not sound. I am using the internal speakers. I have reset it, unplugged it, muted, unmuted, played a dvd movie, but still no sound.
What is the source device connected to the TV and what is the cable type used to connect it? Is the source device connected directly to the TV or through an A/V receiver? Try connecting a different device to the TV - like a DVD player, cable box, gaming console, etc. - and check if the issue still occurs. You may also check if the "Deep Color" option of the playback device is turned on. If the option is turned ON, then turn it OFF.