Having identified a problem of lack of b43 graphics drivers which prevent me from getting beyond a purple screen I've been advised what commands to use to fix this. But I don't know how to access the commands to insert the install command. I can't open Terminal in Ubuntu because I can't get into it. I've been told to press escape when 'grub loading' message appears but I've never seen such a message. Whatever I press on start-up I just get the options to boot either Windows or Ubuntu. Then loads of text ending in the error message for lack of b43 firmware. Then the purple screen.
Can anyone help?