About the AV sources, hook up and if it ever worked.
If optical, always pull the toslink out and give the ports a quick very short shot of canned air. It's something that has paid off for me too often. There are more stories about content downloaded from the web so let's hope this is your bog standard BD player to receiver to HDTV setup.
I have a Yamaha RX-V367 Receiver that I use with my home theater system. The audio drops out at random. When this happens I can regain audio if I push the receiver button on the remote, the movie will stop and screen goes blank. Then push the receiver button again and movie resumes with audio. This can happen when you first start the movie or if you stop to replay a sceen or any other time at random.
Does anyone have any ideas to what is going on?