27" iMac stops on reboot at just over 50% through. HELP!

[PinkyMacGodess]

Upgraded to 10.11.5, and discovered that the 'hot corners' in screen saver don't work. So I unset them, exited Sys Pref, reset them to what I wanted, and no work. So I reboot. It's been stuck at just over 50%, and the screen just went black.

Whiskey Tango Foxtrot!!! What a Charlie Foxtrot!!!

 

[JohnDS]

Try rebooting while holding down the shift key.

 

[PinkyMacGodess]

I held down the power button until it was off, and then started it up, which came up fine. So far.

It's odd that it happened to another iMac here with the same symptoms, and I found no one else with this issue.