Error 404 (WebUI not working)

Hi, I have Raspi 2 with Volumio 1.55
WebUI is not working. It shows a 404 nginx error when I open

I have tried restarting MPD and nginx. (looked over previous posts)
SSH is working perfectly.

404 is a not found error. Have you changed stuff?

I tried installing mate. Nothing else, I think.
What if I did and I don’t remember what I did, is there a possible outcome where I wouldn’t lose my config/data?

You probably did an apt-get upgrade, this is known to cause problems. This is because of dependency hell.
Run the history command, this shows your previous commands.

You could locate and save config files on an other device before reinstalling (re-flash)