kdm try to start but back to the console login

[Franco Gorziglia <franco@gorziglia.cl>]

Hello All,
I´m using Sarge and KDE 3.2
The problem is that kdm try to start al the final of the boot process, 
but then a blank screen and return to the console login. Then, I can 
login as root, and type "#kdm" and kdm starts perfectly. I don't 
understand why it's happens, because if I select xdm as default disply 
manager there`s no problem. If I select kdm as default display manager, 
only after the login as root I can start kdm. I check that the 
"defaul-display-manager" in /etc/X11/defaul-display-manager is 
/usr/bin/kdm I also check that run level is 5 and I don't know what happen.
thank you in advance.