The GUI for configuration shows an absence of any sound devices. Sound works fine for other users.
How do I fix this?
It's broken on purpose so you don't screw stuff up.
The proper way to do stuff with root is to use
Logging in with the root account is a really bad idea, and it's really easy to screw stuff up to the point where you can't fix it. As such, the margin for error is... small at best.
Related: Why is it bad to run as root?