Boot into Gnome. Delete the .kde folder. Then re-try KDE. It is likely a
setting that got messed up because it did not exit properly. Of course you
will lose all of your customisation and settings, but it should work.

Are you using KDE 4.4 with Karmic? I have found that to be a bad mix. If it
is just KDE 4.3 then it should be stable.