[kde-de] KDE problem

[jost.noah at bluewin.ch]

A Nautilus window with Root 
Privileges ? Or rather, the Dolphin with Root Privileges? Unfortunately,
 I've got a Problem. If I use the Terminal to start it and then I give 
su a the the password and after that sudo dolphin or nautilus. 
Error message when Dolphin: No protocol specified
  dolphin: cannot connect to X server :0
Error message in Nautilus: ** (nautilus:2673): WARNING **: Could not open X display
  No protocol specified
  Unable to init server: connection failed:connection refused
(nautilus:2673): Gtk-WARNING **: cannot open display: :0
Can you tell me what Problem it is? Why is that when KDE is not? 
I thank you for coming answers
PS: I am also available in German easy: jost.noah at bluewin.ch
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