Finally resolved this.
Issue:
5K Retina iMac, out of the box did some setup for my client, saw there was an update pending, computer went to sleep. When I woke it screen was black, mouse cursor moves around on the black screen.
- reboot, problem still there
- reset PRAM, problem still there
- single user mode, run disk check, OK, deleten login window plist and boot caches, problem still there
- boot from another mac, voila, mac logs in, so I know the display and hardware is working and this is an OS issue.
-enable VNC and VNC into mac, same black screen and cursor through VNC!
Resolution:
Found another post somewhere of a user who had this on Mavericks and they were able to resolve by hitting tab and typing in the username and password in the right combination on the black screen. Essentially, typing in the username and password blind. So I started typing in the username - tab - password and after the second try BAM - the login window appears. I log in, it then finishes installing the update, and here I am at the desktop again.
HORRIBLE BUG HORRIBLE HORRIBLE HORRIBLE!