There can be 2 reasons for this -- first make sure your streaming in MP3 format, AAC+ does not work in most flash players. You can find this setting under your Centova Cast settings under Mountpoints

The second reason is by far the most common problem for new Centova v3 users. If your music seems to be playing but you do not hear any music, this indicates your server is set to public but you have not yet created the YP Hash. There are 2 things you can do

-- Switch the server back to PRIVATE
  (1) Goto your Centova Cast v3 settings, click on the "Server Overrides" folder tab
  (2) In the dropdown menu under Public Seerver, switch the dropdown menu to NEVER
  (3) Restart Server
you should now be able to hear your music

OR

-- Set up YP Hash
Please follow this video to set up your YP Hash http://myautodj.com/video_tutorials/videos/Centova%20v3%20How%20to%20Create%20YP%20Hash.mp4