No sound from plasma to home theatre

First off it's always best to start from scratch when it comes to home audio. LoL. Many times I've been in this situation.
So with everything disconnected. You should have your HDMI, COMPONENT, RCA(R,W,Y)
HDMI and COMPONENT are the exact same thing and in all preference COMPONENT is far better thand HDMI for the pure fact that each wire is in it's own casing and insualted to avoid feedback from the other wires.
Anyways, with everything disconnected we begin
From you Cable/satellite box- Run your HDMI cable from you cable box to your HDMI 1 input on your tv.(If your speakers were to work on your tv you would automaticaly get sound and picture)
That should be all that you should be running from you cable box. Now that we have one thing running we go to the next thing.
From your TV run your audio out (RCA Red/White) to your amp. Usually your preference but more than likely your TV IN on your amp.
With your amp now set on TV, you should automatically get sound from your tv. and if your running an HD cable box even though your only running RED/WHITE to your amp, you will still be receiving Digital sound.
Most new amps Should have a digital input and if your running and 1080iUp this one RCA plugin will give you dolby digital sound from your dvd player to your amp. Then running a video rca up to your tv, will give you the picture, while the digital out on your dvd player to your amp will give you dolby digital sound.

It's a basic simple step to get sound. Like a continuing current. So just as long as you have your cable to -- tv -- home theatre. Everything should work. Otherwise I would go and check your cables and make sure they are not faulty.
I hope this confusing walkthrough helps.