update: after i deactivated the start script for xbacklight (see post http://forum.ubuntuusers.de/topic/bildschirmhelligkeit-am-acer-laptop-einstelle/?highlight=Tbaustell+Zxbacklight+5235#post-2220005 ) i was able to login with normal mode.
update: forum.ubuntuuse rs.de/topic/ bildschirmhelli gkeit-am- acer-laptop- einstelle/ ?highlight= Tbaustell+ Zxbacklight+ 5235#post- 2220005 ) i was able to login with normal mode.
after i deactivated the start script for xbacklight (see post http://