I found it too, but when I do it, then I have log in GUI but after I log in I have only blue wallpaper and small text console window in left upper corner.

I have a problem. After this above I have GUI login, but when I log in then I have only KDE wallpaper and text console, without panel, menu etc

I thought about this exactly.

But what I have do, if I want login under KDE not in text mode?