For years, I have used a black cable to connect my DVD player to my TV. I think it needs to be replaced, but have no idea what it's called. It looks a lot like those s-video cables, but you just slide it on this silver protrusion, and there's only one thin pin inside, as opposed to multiple.
Sounds like it might be an optical cable. Is it kind of stiff?
I've usually had good luck taking a part in to a store and asking "could I get one of whatever this is, please?" Works more often than not.