I followed the instructions at https://en.opensuse.org/SDB:System_upgrade to upgrade from 13.2 to 42.1. I rebooted successfully into 42.1. When I tried to open Yast I was asked for the root password, which I gave, but then nothing happened. Yast did not show its screen and nothing appeared at all.

How can I see why Yast is not showing anything ? Thoughts ? ideas ?

I do have a backup of 13.2 I can restore to go back, but I would rather get 42.1 working correctly.