"Oh no! Something has gone wrong."

Hello, After a failed attempt to install the manufacturer's nvidia driver, my system (Fedora 19, with both Gnome and KDE, on a Lenovo ThinkPad T430) does not reach the graphical login screen any more, but instead ends up in a white screen with a frowning computer cartoon and the message "Oh no! Something has gone wrong. A problem occurred and the system can't recover. Please contact a system administrator." I can still do Ctrl-Alt-F2 to log into text mode. When I try startx, I get an empty screen with white or black background and a mouse cursor, extending over my two screens (laptop and external). When I try startkde it says: $DISPLAY is not set or cannot connect to X server. The only error in /var/etc/X11.0.log is: Failed to load module "nv" (module does not exist, 0) In /var/log/messages, there are a bunch of lines like (I'm typing by hand): gnome-session[2658]: (gnome-shell:2949): Cogl-WARNING **: ./driver/gl/cogl-framebuffer-gl.c:561: GL error (1282): Invalid operation Could not find a solution on Google. I already reinstalled a bunch of packages, including cogl, gdm, gnome-shell, @kde-desktop, xorg-x11-drv-nouveau, kernel, but no change. Any advice? Thanks! Best, Oliver -- Oliver Ruebenacker IT Project Lead at PanGenX (http://www.pangenx.com) Be always grateful, but never satisfied.