Problem solved:
1) I deleted the .htacces – file in the root folder of wordpress
2) I deleted in the database, table wp_options, Entry ‘permalink_structure’ the value, so the field was empty
3)
I renamed the folder root/wp-conten/plugins
to plugins_
4) Yipeeee!
I had access to backend and frontend
5) I renamed the folder root/wp-conten/plugins_
to his correct name plugins
6)
Activated all plugins and reinstalled all plugins where the activation does not work
(the only problem I have is the YOURLS-plugin for Twitter, but I am shure to fix this, too)
Thanx to all of you, this forum is live worth!
pilaster