Chosen Solution
After upgrading to 10.13, mid-2012 Macbook Pro keeps getting No Entry symbol on boot up. Thought the SSD failed, replaced it with new SSD. Formatted drive, Apple checked hardware with their diagnostic tool. No problems found. Downgraded to 10.12, and still getting stuck in a No Entry/Apple Logo loop cycle for about 5 minutes, before it sometimes deciding to boot up. Link to bootup: https://www.youtube.com/watch?v=rjC0fPfh… I am not sure what to do next. Please advise.
Basically, the prohibitory symbol means your Mac couldn’t find a valid System Folder to start up from. This could be quite simple once you get the system to boot up using an external boot drive (if you can’t get it to boot up). To fix it you’ll need to get to the systems preferences and locate the ‘Startup Disk’ control panel and then select your internal drive and restart (removing your external drive as its restarting). That should fix it. Update (03/27/2018) Well, if thats the case then it must be a bad HD SATA cable. The cable is known to fail a lot at it rubs along the rough surface of the uppercase. Mostly we see the folder with the blinking question mark when if fails. Here’s the IFIXIT guide: MacBook Pro 13" Unibody Mid 2012 Hard Drive Cable Replacement and here’s the needed part: MacBook Pro 13" Unibody (Mid 2012) Hard Drive Cable. I would add some electricians tape where the cable rests so it gets a bit more protection also don’t over crease the folds as that can break the foil wires inside the ribbon cable.
