I have same issue in SUSE10. After many times loged in as root suddenly lost that option. Of course I did log in trough console shell and startx gives me KDE normally. However when wish to close KDE session many strange messages came back to console shell and finally lost posibility to type in anything into console. One of last messages was that x server is killed.
Attempt to start new session Ctr+Alt+F2 and login again in order to poweroff machine how I could kill previous unmanagable console shell.
Also could power off trough remote terminal connection what is basically the same.