DELL 4500 S CPU with Harmony-Kardon speakers

A few days ago I noticed that my sound had diminished to about one half its previous volume. I upped the manual indicators on the Sound Horn, upped the speaker volume knob, and upped the Real Player volume control as well.

Today I get no sound what so ever.

Is there any way to troubleshoot my problem ??

I have re-installled my audio drivers from the original DELL CD and I have tested my Harmony-Kardon speakers on both my TV set and my electronic piano and they perform perfectly.

The computer gives me this ERROR message which says :

" No Audio Hardware is available or the hardware is not responding"

Thanks for any help...