Close Lightroom if it is running.
In Windows Explorer, go to C:\Users\Your ursername\AppData\Roaming\Adobe\Lightroom\Preferences
There will be a file called Lightroom 6 Preferences.agprefs, open this file in a text editor.
Very close to the end there is a line that says useAutoBahn = true,
Change this to useAutoBahn = false,
Save and close the file, now try to start Lightroom.
thanks alot, it did the trick, BUT:
after changing tue to false; LR when started changed it back; after 2nd attempt I could tick-off the Bearbeiten/Voreinstellungen/Leistung - Grafikkarte
now seem to run (albeit changing from Bibliothe to Entwickeln takes a few secs
If the problem comes back, take a look at this article - Turning off Lightroom’s GPU preferences even when crashing on startup. | Lightroom Blog
that suggests restarting the computer before editing the preferences file, which will clear preferences stored in the computer's memory.