It should come as no suprise that you can't autologin to kde without a monitor.
Kde is a graphical environment, which means it needs a monitor to display.
Which means that the graphics card needs to communicate with that monitor to display.
Which means that without a monitor to display what the graphics cards sends to it, it won't autologin.
Which means that you need to do some google research on how to autologin to runlevel 3.