Home Theatre - No sound from any speakers?

I opened the DVD player to clean the lense and since then no sound is coming from any of the 5:1 speakers. I think the DVD is simply not outputting the sound to the speakers. When I connect using "old sytle" cables to TV - I get sound from the TV speakers. Also looking the DVD LCD screen it should normally show all the speakers connected but in only shows 2 Square brackets "[ ]" (one on top of the other ) Obviously all speakers are connected properly ! Any ideas ?