I recently upgraded my Toshiba Satellite P105 laptop from Ubuntu 11.04 to 12.04 (I don't have windows there). It was working fine for a couple of days, but now every time that I start the laptop, I get a black screen that says GNU Bash (it looks like the operating system command screen). I can't find the exit command to close that screen and to continue starting the regular Ubuntu. I would appreciate some help, and please write what I have to do in plain English, I am a normal person (a mechanical engineer) not a computer scientist.
Thanks in advance for you help.