a very annoying pb with accounts

[Grégory Nou]

Hi everybody,

Here is my (weird) problem ...
I opened /etc/spwd.db with ee and exited (which was actually a very bad 
idea, even if I did not modified anything). At this time, everything was 
still ok.
Then, a few minutes later, I tried to su ... Impossible : I get some 
weird error message telling me "su: who are you ?"
Then I tried to log directly from the login shell on tty0 with my 
account... unknown user.
I add a look at /etc/passwd : everything was correct.
And when I tried to recreate my account : "user already exists"
Then I reboot (the second very bad idea in the same day), and user "gdm" 
didn't exist anymore.
Exactly as if I forgot to make mergemaster after upgrading, but with 
only one difference : I actually didn't made a upgrade.
So now the situation is : I can only access with root account.
Does someone know when I did a mistake ? and does someone knows how to 
fix it ? Should I delete account in /etc/passwd and create them again ? 
I had this idea, but I didn't want to make another stupid thing today :)
Thanks a lot

-- 
Gregory Nou