no sound from dvds but ok with cds

[Garfield1]

I have a Sony ke-32ts2e and a dvd player dav-sa30 compact av system.  Just to warn you that I am a girly so this won't be techy but desperatly need some help.

I cannot get sound from the dvds but ok from cds, but I used to be able to.  I noticed that there is a cable, that I may have inadvertently moved.  The cable is grey in colour with 2 jack plugs either end, one black one grey (on both ends). I really don't know where they are meant to go.

I have sky, and that has two ports it could go in to; one says left one says right. The back of the tv is rather complicated as is the back of the dvd player.  I haven't a clue where they should be plugged in. The cds play without this cable at all.

Oh please someone help me!!

thanks