Late 2012 Mac Mini random restart and prohibitory symbol (circle with line through it)
Late 2012 Mac Mini randomly restarted and displayed the prohibitory symbol (circle with line through it). A Mac user since 1984, I’ve never seen this symbol. I backup with Time Machine to an external drive. Did it try to update the OS? I did not update, so I am a version it two behind, but I can’t determine the OS. Please advise.
Mac mini, macOS 10.12