Installation not possible - it stops - now login failure

Hallo, after starting the installation process, this stooped for a long period. I started it again, but nothing happens.
Actually i cannot login in backend of site - that is a really big problem.
On top of login-field the info:
JAuthentication: :__construct: Die Authentifizierungsbibliotheken konnten nicht geladen werden!

What the hell is your extension doing?
Please give me an info, how to fix.
Thanks a lot
Best regards
Frank