Trouble with audio

I am using the latest version of the Blankslate theme. I am using my own CSS, added a couple of widget areas, and a customizable header image. The only problem is that I cannot get the default WP audio player to work (I’ve tried using the shortcode [audio] and simply pasting the link), nor several other audio plugins. The mp3 files won’t play. They show up in the text editor, but are empty spaces when I preview/publish the page.

Does anyone know what the problem might be, or if there’s a theme function that I can add to make the audio work?