Might try a different use if that works then
You can try resetting the kde configs I guess just rename the ~.kde4 folder but you can't do that with running as you. Best way log into a console as root (press ctrl-alt-F1) type init 3 to shut down the GUI type

mv /home/yourusernamehere/.kde4 /home/yourusernamehere/.kde4.old

type reboot

that will bring thing back to day zero on the GUI configs.

If different user does not work we need to know what card/driver you are running.