Why can't i get any sound on my set-top box?????

how do you expect us to help if you don't provide any details? we aren't psychic.

-what pieces you want to connect. (might as well list your whole setup)
-what cables you have and how you have it connected now
-what you have tried already
-any settings you have changed from default

without any details any information given will not be tailored exactly to your situation.