Only some of my speakers are working on my home theatre system?

I have a sony home theatre system complete with dvd player, sub, 2 big speakers, 1 medium and 2 small speakers mounter high.

Now when I plug them all in only the 2 big speakers and my sub work.
The thing is when I plug the small speakers or the medium into the slot where the big speakers are suppose to be plugged in,they work so its not the speakers .

any solutions?
Thanks!
 
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