open tty1 by perssing CTRL+ALT+F1
login as root
run this command:
logout by typing 'exit'
go back to graphical by pressing CTRL+ALT+F7
If that doesnt work, instead of reconfiguring it, try purging it then reinstalling it:
apt-get remove --purge kdesu
apt-get install kdesu
If purging, take note as to what programs might be purged with kdesu because of dependancy issues. If too many will be purged, might not
want to try it.