When I start my computer krusader open 4 screens. I can't find where this to disable.

First of all, you must know that KDE have session support through XSMP, so if you poweroff your computer with open Krusader, you will get it on next startup. if you want empty new session must select "Start with empty session" in second dialog.

I close krusader before shutdown computer. I go try your tip.

Pretty sure this is an upstream issue with porting krusader to kf5.

I have seen the same behavior, no normal settings stops krusader from auto-starting.

Give it a little time, see if this is fixed with the ongoing port that is taking place, or open a bug report on KDE for frameworks5 based krusader.