Help! Why can't I still get a surround sound?

I’m totally flummoxed. I’m not in any way tech savvy but I do my best to catch up. Not enough. I still suck.

See, we just purchased these :

40” Sony Bravia LCD TV
PS3 with BluRay disc player
Sony Bravia Home Theatre System

I connected the TV with the PS3 with an HDMI cable.
I connected the Home Theater to the TV with an HDMI cable and an optical cable.

I put in a BluRay disc to the PS3 hoping to get the two surround speakers located behind me to work. They don’t. Also, the center speaker doesn’t work. Only the subwoofer and the two side speakers do. What am I missing?

Would appreciate all help I could get. Thanks.