I've had the worst luck with KDE. All the new updates always screwed things up. I went to xfce but then that was always blanking my screen. I did this:
I rather liked the simplicity of the following remove:
apt-get remove kdelibs-bin kdelibs5-data
Credit to craigevil on the Debian Forums. (http://forums.debian.net/viewtopic.php?f=10&t=102884)
The thing here is that, by focusing on the two packages on which virtually all of KDE is built, the rest of KDE gets uninstalled too, as they depend on the above.
Then I did aptitude autoclean, and reinstalled with aptitude kde5 (I think). Anyway, it all works perfectly. Better than reinstalling, which I've done before for this.