Is there a setting on the projector that controls sound output? I suspect there is and that it's off by default. I'm also assuming you're connected via HDMI? We need a bit more info in order to give you sound advice (no pun intended).
What is the model number of the blu-ray player?
What is the model number of the projector?
How are the two connected (what cable)?
Is there an audio system involved?
If so, what is the model number of the audio (home theater) system?
Is there a setting on the projector that controls sound output? I suspect there is and that it's off by default. I'm also assuming you're connected via HDMI? We need a bit more info in order to give you sound advice (no pun intended).