Sound not working in PowerPoint Presentation

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Possibly an issue concerning 'Linked' or 'Embedded' music:
Use embedded and linked sound files in PowerPoint - PowerPoint - Microsoft Office

The differences between linked and embedded objects

The term "object" in this article refers to a sound (including a piece of music). An object can be the sound itself, or it can be the file that contains the sound.
The main differences between linked objects and embedded objects are where you store them and how you update them, if need be, after you place them in the destination file (in this case, your presentation).
Linked object A linked object is created and stored in a separate source file, and then it is linked to the destination file. Because the two files are linked, when you make changes to one file, the changes appear in both the source and destination files.
Embedded object An embedded object is created in a separate source file too, but then it is inserted into the destination file, becoming part of that file. If you make a change to the original source file, the change will not show up in the destination file.

An embedded object
A linked object
The source file that contains the linked object
How to choose the best file type

Let's say you've created a presentation to which you've added several music files that act as a soundtrack. You've set up all the transitions and timings and such, and it works like a charm on your computer. Here are a few questions you need to ask yourself before considering this project finished. In fact, you can save yourself a lot of time if you think about these things before you add your sound files.
How big is each sound file?

Use these criteria to choose a file type based on size:

• If each individual sound or music file is 50 megabytes (MB) or less, you can insert it as either a linked or embedded object. (Note that embedded objects larger than 100 KB may slow down the performance of your presentation, however.)
• If your file is more than 50 MB, it should be linked — it won't play in your presentation if you embed it. The default setting in PowerPoint for the allowed maximum size of embedded objects is 100 kilobytes (KB), but you can change it to a maximum of 50,000 KB (50 MB).

How do I change the maximum size allowed?

1. On the Tools menu, click Options.
2. On the General tab, increase the Link sounds with file size greater than ___ Kb setting to a size just larger than your largest sound file, up to 50,000 KB (50 MB).
3. Click OK.

Lots more information in the link at the top of this post. :)

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What format is the audio? - it seems that wav files are best:
How to Embed Music in Powerpoint | eHow.com