Stuck at login

Yosemite install went fine until it showed "about a minute left". This took about an hour, but I didn't mind. However at the restart it stuck with a beachball. After waiting for over an hour I powered it down, restarted and it worked up to the Login. After entering the password it was one again stuck wirh a beachball.
I tried everything I know: SMC reset, PRAM reset, fixing disk permissions. I did another install (again about 40minutes with "one minute left"), this time it went to the login without problems, but then again, stuck with a beachball after entering the password. Any Ideas?

 

Guess I am not the only one. http://osxdaily.com/2014/10/17/os-x-yosemite-installation-stuck/

And another one: https://discussions.apple.com/thread/6601935?start=0&tstart=0