Computer start menu/toolbar gone...and comput

Hello,
My computer, which has windows xp, was working absolutely fine, and then after we shut it down that night, and restarted it the next day, our background picture comes up..but nothing else. No start button, or toolbar. If you put a cd in nothing happens...you hear it spinning, but nothing comes onto the screen, if you press ctr alt del..again...nothing. Also when you start it it now bring you to the login screen...which we did not have before, so something changed that also. Is there hope? I would really like to not lose all of our files!!