I accidently deleted my main menu bar with the system, application, etc. . How do I restore it?

Just open the terminal and run the coammand
rm -r ~/.gconf/apps/panel
Now re-login!

How to restore gnome panels and toolbars disappered on Ubuntu

A) When you see the clean desktop without toolbar:
- press alt-f2 a little window will come in fron of you
- ins this window field type:

gnome-terminal

Then press enter a terminal window will come in front of you:

type (a single row a time then press enter) :

gconftool –-recursive-unset /apps/panel;
rm -rf $HOME/.gconf/apps/panel;
pkill gnome-panel

B) if you cannot get access to terminal using method A then:
- press ctrl + alt + F2 you will get a pseudo terminal black screen in front of you
- Make login with your user and password (when you type the password you will not see any screen chars, so type in then press enter)
- then when you get access, type (a single row a time then press enter) :

gconftool –-recursive-unset /apps/panel;
rm -rf $HOME/.gconf/apps/panel;
pkill gnome-panel

Then press ctrl + alt + F7 to return to your desktop

Hope this helps

New to Ubuntu: read the Ubuntu Manual, it's very informative: http://ubuntu-manual.org/
Click on the "download Button" to download the latest PDF version.