Debian and most of its derivatives use runlevel two for everything. To get back into the equivalent of runlevel 5, you would have to do as root
#/etc/init.d/gdm start (replace gdm with kdm if you use kdm)
To stop the xserver like runlevel 3, you would do something like
There is a way to make sure that you always login to a gui. I think it involves using dpkg to reconfigure the xserver.