As for the root terminal -- as have been pointed out, open a regular terminal (press Win key, type "terminal", enter), and type
sudo -i, then your own password. But beware, you can trash your system as root if you don't know what you are doing.
Something must be wrong with your language / keyboard settings.
- What physical keyboard are you using? US, German, ...?
- Go to System -> Preferences -> Keyboard to open the Layouts tab. Move the appropriate layout to the top.
(in 12.04 - press the "Win" key, type "keyboard layout", Enter. Make sure that your layout matches your physical keyboard. There is a little icon of a keyboard below the options. If you click it, you will see what the chosen layout is. I assure you that the @ key is there, waiting for you to get pressed)