Chosen Solution
I too have this issue on a mid 2012 unibody MBP. It was running a Samsung SSD, flawlessly for years (purchased 2016), then it crashed one day last week and wouldn’t start. I got the folder with a ? in it and went through an internet recovery, whereupon, after downloading the OS, the machine restarted to the prohibitory symbol. I installed a brand new Samsung SSD, formatted it to journaled in disk utility and then downloaded the OS again, assuming the 8 year old previous SSD (which I had used in previous iterations of MBP) had developed a fault. Same thing happened - it restarted to the prohibitory symbol. Perhaps tellingly, the original SSD, when placed in a caddy enabled the Mac to start up as normal through a USB cable. I therefore suspect the issue is a SATA cable failure, as you imply can be a cause. What’s your view based on this description? thanks. Damian.
Yes you need a new HD SATA cable! Here’s the needed part MacBook Pro 13" Unibody (Mid 2012) Hard Drive Cable and here’s the guide to putting it in MacBook Pro 13" Unibody Mid 2012 Hard Drive Cable Replacement Here’s a bit more on the issue: Your Hard Drive Cable Is A Ticking Time Bomb Besides the tape you want to find an old BIC ball point pen to get the ink straw out of it as you’ll need it to help you bend the cable as a brake form. You don’t want to crease the cable as that also damages it! Use the straw to help you create a nice smooth arc as you not want to exceed the radius of the straw.
