Try:
Menu-->System Settings-->System Administration-->Login Screen-->Theme

And see if you can set the login screen to something that shows up. The Lovelock theme is default, make sure it's either set for that, or, see if one of the others works.

When you get a chance, please explain what you mean by crashed. Exactly what is going on, what do you see during that crash? Or have you worked it out?
Sorry I had a long day at work and didn't see your post earlier.