I got problem with nautilus in Ubuntu 12.04 LTS

when i run command "gksu nautilus /" password ask box appear and I type my super-user password , than password box is disappear and nautilus is not open. .

when i try to open nautilus via normal user in command box . "nautilus" the folder is open up.

when i try in terminal ...

$sudo nautilus

I got following error

$ sudo nautilus /

** (nautilus:8523): WARNING **: Command line `dbus-launch --autolaunch=2c8ce9b7da2257c2609b749700000007 --binary-syntax --close-stderr' exited with non-zero exit status 1: Autolaunch error: X11 initialization failed.\n Could not parse arguments: Cannot open display:

how can i fix this error..