Reporting back.
I used our LiveCD and
chrooted into Mageia.
Lightdm was the displaymanager that caused the problem and reinstalling it did not help so it was time for some Berserk style actions
I deleted lightdm and installed lxdm.
Then I enabled the Lxdm loginmanager like this:
Jumped out of chroot with CTRL+D and unmounted mageia.. and rebooted.
There i was prompted to log in by Lxdm
and
It logged me in perfectly fine.
Don't ask me why Lightdm suddenly stopped working though (Maybe a policykit thing) anyway I don't care as long as i can log in and continue to destroy my installs...

I noticed that
Lightdm has been misbehaving for a long time in Mageia, at least with with XFCE4 and Cinnamon so this is kind of a solution (aka workaround)...
