Thank you! I didn’t look at the right place!
What really was the most helpfull point in the troubleshooting: I did not have the right editor!
Everybody with the same problem (seems to be quite common):
1.
activate your php-error-messages (then there is no white/blank page anymore, you get a nice error-information instead)
2.
Check the search above, paste your error there
3.
you find the advice to remove White lines an spaces in the wp-config.php – I was not able to find any, because I did not use the right editor – not every editor shows them! (I used one from microsoft and it did not show me spaces). When I opened the file with another Editor (called Phase5) I was able to see and remove some weird signs in the first line. Then upload the wp-config.php again.
Thanx!
Andrea