Title says it all, really. For some reason, there are absolutely no settings available in the System Settings app:

No settings :(

Even if I go into the settings via other apps, they still don't appear. When I installed gnome-system-settings , they showed up in that app but didn't work.

I've tried reinstalling ubuntu-desktop , but I'm pretty sure that only works for 14.04.

Any ideas would be much appreciated.