Post originale di: mayer ,
I experienced this on several machines in the last couple of months. It is my personal belief the Apple has caused it in their system upgrade with High Sierra on machines that have ANY third party upgrades (RAM or hard drives. So far I have been able to get all of them running again by booting from an external drive with El Capitan installed. Next I removed the internal drive and wiped it on another machine then installed El Capitan. One 2009 I had to take back to Mavericks.