A somewhat brutal way is to log in via Gnome, then using a Terminal (e.g. xterm) an moving your kde-directory ($HOME/.kde) to something else (e.g. "mv $HOME/.kde $HOME/kde-backup). After that you log out and log into KDE.
With this method you loose all your settings etc. in KDE, but at least you get your keyboard. But, because you only moved your prior KDE-directory you may get your settings via the Terminal again. At least it's the fastest method for your problem
Debian Linux, mix of stable, testing and unstable; KDE with Compiz Fusion >=0.52 (git)