Quote Originally Posted by harald612
.... KDE works fine, using the Live-CD.
........
Now, after installation on my harddisk, switching in graphic mode is not working.
Lots of stuff keeps breaking when Knoppix is "installed", this has been going on for years. The forums and wiki are full of warnings against it. Now we have news that Klaus is even considering finally removing the install script completely. The obvious fix for your problem would seem to be to install something that will not cause problems by it's very nature. Debian Etch would be one suggestion, although there are others.