Unless you have the internal mute enabled (or "external speakers" selected in the audio settings with no external connection), then it's likely that you may need to have the unit serviced. I would recommend calling Samsung's customer service center in your region.
My TV has been taking longer and longer to turn on. Today there is no sound at all. I have tried different components, Foxtel, DVD, Media Player and I get a picture but no sound. I also tried to watch through normal channels but even though TV says they are there, there is no picture or sound. I have tried to reset TV and have unplugged it for 10 minutes and then tried again but still nothing.