I'm setting it up again with the dvd.
I'm trying to setup a Media Director. But it isn't a thin client.
If I want to install linuxmce he tells me, that there is already a core in the network, so I chose only to install linuxmce.
After that there is the advice to restart the computer. If it's booting again, the computer automatically boots Kubuntu again!
What ist wrong, or what can I do to fix the problem?
Once you have a working hybrid Core all you need to do is set the PXE boot options in your chosen MD's BIOS and attach it to the LAN side Nic via a switch and it should auto detect and add itself. look on the Wiki for the details of this.
The MD only minimally needs; motherboard, processor, 1gig RAM... optionally you can add an optical drive if you want to play CD/DVD's live from the drive or if you want to use the MD ti rip audio or DVD content and store it on your Core or somewhere else on your LAN. The MD can also have an HD too... in which case this too can be autodetected by the Core and then added to the available storage on your system. Again see the Wiki for more info on these options.
All the best