For sound dropping out the most common cause is other than stereo or PCM audio feeds. Easy to fix, set it all to stereo.
As to shut off, can't tell age and more. Just like out PCs I get out the canned air. Owners that ask what is canned air answered so many questions.
Bob
Lately the sound disappears for 5-20 seconds while I watch. Happens 2-3 times/day. The TV also shuts itself off while I am watching, 1-2/month. Fine when I turn it back on. Is this due to age or can it be fixed?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic