When you send your PowerPoint to other computers, do remember send the music file togeter. Then reinsert the song to the presentation to make sure it will play normally.
Also, you can convert your PowerPoint to a video first (all the elements in the original PowerPoint will be retained, like songs, animations, etc), then you only need to send the video file to other computers and the PowerPoint will play normally.
Tool you can use: Wondershare PPT2Video (http://www.ppt-to-dvd.com/ppt-to-video-overview.html#242 )
Hope it helps.