Cannot login as root in terminal

[Jon Jahren]

Hi.

I'm having a problem changing from my user "jon" to "root" using su -,
it worked before, and it stopped working after my computer mysteriously
locked up. I can use my root password to log in via gdm and install rpms
via the gui, but if I try to change to root in a gnome-terminal I get
"incorrect password", I've tried disabling selinux, and I can't find
anything in the logs about it. Any help appreciated, thanks.
Regards
Jon Jahren