Hi,
Try logging on console ALT-CTRL F1 as user or root and try to start KDE using
You may need to do something like:
Code:
# kdm --nodaemon
# pkill kdm
Just not to restart kdm or different diplay manager you use (gdm, xdm)...
after that post content of .xsession-errors file that you find in home directory of affected user.
It may be also helpful if you send content or last 10 lines from /var/log/Xorg.0.log file.
All the best.