I recently purchased an M-Audio M Track USB Interface, and when it's connected sound and video files won't play on my mac.

As mentioned above I have bought an M-Audio M Track USB Interface and when I select it as the Input and Output for my Macbook Pro I can no longer play video or audio.

I've tried playing files in iTunes, I've tried playing quicktime videos, and running youtube videos but none are playing when the interface is plugged in.

When I change the output to internal speakers, videos etc are playable again.