System settings have disappeared

Hi all,

Most of my System Settings have disappeared, and I am trying to figure out how to recover them. For some time, I have only been able to see "Passwords", and now, after installing a Seagate app for a new external HD, "Toolkit" appears, but nothing else. See attached screenshot below.

Any help will be gratefully received as I live in a country without Genius Bars to seek help from.