I got it fixed.
The problem was not the keyboard, but the flash card reader (via internal usb)
I got messages like "device not accepting address 4, error -110" in /var/log/messages.
Solution:
- Log-In
- disconnect the card reader from pc (plug out usb connector)
- reconnect the card reader (maybe you want to start "tailf /var/log/messages" before)
The next boot was really fast and the keyboard was immediately recognized and the mouse, too.
Greets