Black Screen With Cursor on Logout in Yosemite
Just returned here, although old question, to leave the solution I have found  after long suffering this problem in High Sierra after trying to upgrade from version 10.13.5 to 10.13.6. I deleted these files through terminal, then rebooted. 

You may need to enter your admin password when asked:

sudo rm -f /Library/Preferences/com.apple.loginwindow.plist
sudo rm -f /private/var/db/.AppleUpgrade
sudo rm -f /private/var/db/.SoftwareUpdateAtLogout
sudo reboot