Media not found? Powerpoint

I've just spent hours putting together a powerpoint, trying to make it funny and engaging for the kids I work with by adding sound effects I found in powerpoint and online. I just went to work on the project today, and while all of the sound clips I found on powerpoint are working, all of the sound effects I downloaded will not play. When I mouse over the speaker icon on those slides it says "Media not found". Where did my sounds go??? Just a couple of days ago it worked fine! I didn't even close the project; I left it open on my desktop because I was afraid I'd lose something if I did!

If you didn't save your project including the sounds before you either shut down your Mac or rebooted, they're now gone. For best results with any Office file whether it be PP, Word, or Excel, make sure you have auto save turned on and "always make a backup" selected in Preferences, Save.