I have used a song from my library for my slide show. When the song ends, there are still slides left with no music. How do I make the music play in a loop?

If you haven't figured this out here is what I do for powerpoint 2013...

1: Select the audio element in the slide.
2: Right click it.
3: Select Timing.
4: There is a repeat option and then select however many times you want it repeated.

Hope that helps.