重置gnome panel

 Once the Terminal window opens, enter the following command at the prompt:

gconftool-2 --shutdown

(Note: There should be no spaces between the two dashes before shutdown.)

EDIT – Reader nickrud has suggested a better method instead of shutting down gconfd. Instead use the following command (thanks nickrud!)

gconftool-2 --recursive-unset /apps/panel

(Remember: There should be no spaces between the two dashes before shutdown.)

Then enter the next command:

rm -rf ~/.gconf/apps/panel

And enter one more command:

pkill gnome-panel