Re: system and preferences menu not showing in menu bar.
Ubuntu 11.04 and above do not run the old Gnome 2 software. Instead, the desktop environment in use is Unity, and it doesn't have the same menus as Gnome 2.
You can access system settings through the top-right menu (the one that looks a bit like a cog and a power button) and going to System Settings.
If you right-click on the Ubuntu button at the top-left of the screen, and click Applications, you can bring up a list of installed programs. Some of these used to be in the System or Preferences menu in Gnome 2.
I try to treat the cause, not the symptom. I avoid the terminal in instructions, unless it's easier or necessary. My instructions will work within the Ubuntu system, instead of breaking or subverting it. Those are the three guarantees to the helpee.