problem with user log in

[Enrico Pisoni]

Hi
yesterday I updated my Fedora Core 3 installed on a single cpu-pc, and 
it happened a very strange thing...

Now I can login only using "root" account....if I try with simple user 
account, the system stops on a blue monitor....and nothing 
happens....and nothing can be done....

But if I log in as a root, I can enter in the shell, change user, enter 
in my home and work normally....but only using shell

someone can help me?
thanks
Bye
Enrico