Slackware Nvidia two displays - Black screen after sleep or restart X


Is this KDE4 or Plasma 5?

Remove the folder

~/.kde/share/apps/kscreen/ or

~/.kde4/share/apps/kscreen/

(depending on your distribution) for KDE4.

Or remove

~/.local/share/kscreen/
and
 ~/.kde/share/config/krandrrc

for Plasma 5.