Question about playing sounds in (stream) sync

Hi there,
I’m working on an animation project, and it was my first time to work on flash cs4, I faced a problem when I import a sound file (.mp3) or (.wav) and change the sync into (stream), I used to do this step in the last version in flash to play the sound when I drag the slider to right or to left, but now I can’t play it, any one can help me in this?
Thank you.