Phillips Home Theatre System

When I initially set up my home theatre system, my DVD player, VHS player, CD player and TV all worked perfectly -- the sound was great with each different component and I had no problems at all.

Then for a reason that I cannot discern, the sound for everything except the CD player vanished. My daughters were home visiting, both are pretty technically savvy and both assured me that they had "touched no dials" on the receiver and therfore had no ideas as to the vanishing sound either.

After days (and nights) of intense dial manipulation and button pushing, I finally just turned on the sound on my TV so I could at least watch that, but have yet to be able to watch a DVD or VHS tape. I had a friend come and pour over the manual for the system and he swears that someone had to have pulled something loose but then could find nothing out of order on the back of the receiver.

Am I doomed to never watch a DVD again? Is it logical to believe that if the system was really broken, all sound would have vanished rather than just some sound? HELP!!! I am looking for any and all suggestions to my dilemma!