This seems to be a popular problem in kde’s history, after an update your menus and general look & feel of your desktop is just weird (actually is just without any theme). Trying to set a theme again it won’t work. To fix this you just have to remove one file and regenerate the cache config with another command, just execute:

$ rm ~/.config/Trolltech.conf
$ kbuildsycoca4 --noincremental

Then restart your session (or close your apps and open them again) and there you go, pretty again!