can't log back in after logging off

[Matyas]

Hi,

I have a Windows XP Pro (with SP1) running on a Dell
Inspiron 8200 laptop.
Oh and it is part of a domain.
Two people use this machine, and they, of course, want to
use their own
credentials. So, they want to log off and later the other
one wants to log
back on. But for some reason, the user interface never
comes up after the
user logs back on.
I even reinstalled the whole computer, updated the BIOS,
downloaded
everything from the Dell website, but the problem just
doesn't want to go
away.
Any idea???

Thanks,
Matyas