Hello all,
Just for the record.
I googled "$DISPLAY is not set or canot connect to the X server" and found these pages
http://forums.gentoo.org/viewtopic-t-852063.html https://bbs.archlinux.org/viewtopic.php?pid=846216
they pointed me to
sudo rm -rfv /var/tmp/kdecache-<user>
the second page said that it "is enough!", but it wasn't in my case, KDE still does not work.
Then I also proceed to
sudo rm -rfv /tmp/kdecache-<user> sudo rm /tmp/.Xauthority* (just paranoid)
and reboot.
Some (or all) of those last commands solved the problem, now KDE returned normally.
Thans Joe and Mat for the support.
Best regards.
Waldemar