Mavericks Black Screen with Cursor (mouse)

Just encountered two Mac Mini's which, when turned on, show a black screen with a cursor which moves when you move the mouse. cmd + alt + esc doesn't do anything.

Tried:

1. reset PRAM
2. SafeBoot (hold down shift)
3. hold down cmd + s and type "/sbin/fsck -yf"

I gave up and reimaged these macs.

Did a bit of research afterwards and found this apple discussions on it. There were two suggested fixes. One involved blindly logging in which isn't an ICT Technician friendly fix. However, Spiro.r suggested:

1. ssh 192.160.0.1 -l username
2. sudo rm /Library/Preferences/com.apple.loginwindow.plist
3. sudo rm /Library/Preferences/loginwindow.plist
4. sudo rm /private/var/db/.AppleUpgrade
5. reboot


As ssh is by default turned off, you could also do this in single user mode (hold down cmd + s).

Apparently it is a problem with updates. It basically wants you to log in and OK an update, but seems to stop the login screen appearing. Not entirely sure anyone knows what's happening, but deleting these preference files and .AppleUpgrade fixes it. I shall try it next time I see it.