So, that proprietary 3D graphics driver you installed is now causing you some problems, so you got rid of it. But there's a problem. Your KDE 4 installation had those fancy desktop effects enabled, which now aren't working. Instead of a KDE desktop, you have a nice white screen. There is an easy keyboard shortcut you can use from within KDE to quickly toggle the desktop effects on and off if you have a problem with them which causes KDE to be unusable.