KDE doesn't start automatically

[lorenzo zampese electrolux it]

I installed the Red Hat 7.2 (Enigma) i386 with kde windows manager.
Then I made the kernel matching my hardware.
After this I started the X windows system using the 'startx' command and
all was ok.
Now after the first launch of the X windows system, when I run 'startx'
the x server start correctly (I can see the graphics background) but the
kde windows manager doesn't
start.
If I open a 'xterm' session and I type "startkde" manually, the windows
manager start correctly....

Why doesn't kde start automatically ?

Thank you.