Many Ubuntu users would customize their gnome desktop by changing the default panels with dock or AWN.This tutorial shows how to restore this default panels.

First,open terminal from Applications->Accessories->Terminal.type this command and all panels will disappear.

gconftool --recursive-unset /apps/panel

then,type this to delete current one:

rm -rf ~/.gconf/apps/panel

Finally,reload panel:

pkill gnome-panel