DirectX audio problem

Hi I can get audio working fine - however I can''t get 3D sound to work at all. If I play the music segment infinitely it works fine - then when I update the position of the listener using the call buff->SetPosition(x, y, -z, DS3D_IMMEDIATE); no sounds can heard at all - regardless of the positions of xyz. I can even set the x,y,z to be at the same positions as the initial positions and the same position as the sound in the above call but still nothing comes out. I''ve been stuck on this for a week now !! HELP !