Intermittent Prohibitory Symbol on Boot

Howdy, fellow iFixiters,

Ok so, I have a 13” Mid 2012 MacBook Pro in my shop with an interesting issue.

The MacBook Pro has an upgraded ADATA SSD and upgraded ram.

So, this computer was first brought to me because the owner forgot her user password and she wanted me to reset it her for her.

So, I attempted to use single user mode on boot to create a new admin account which I could then use to change her user password with.  However it kept giving me an error in Single User Mode regarding not being able to mount the FileSystem.  I was trying command: /sbin/mount -uw /

Ultimately I resorted to booting into recovery mode and using terminal to do the trick.  No problems.

However throughout this process I ended up running Disk Utility and found a persistent error on the SSD about the EFI partition size, or such.

I returned the computer to the client and explained that I was able to reset the password, but there does seem to be something amiss with the SSD, and potentially a new one could be in order, eventually.  She understood.

So, last week, the client let me know that the computer now shows the flashing folder on boot.

This was something a saw happen when the computer was first in the shop, however, I was able to set the default startup disk as the SSD and all was fine

So, the computer is back in the shop now and I was able to get it to boot if I hold option on boot and select the main boot drive.

I then ran first aid in disk utility and got this message:  “Problems were found with the partition map that might prevent booting.  The partition maps needs to be repaired because there’s a problem with the EFI system partition’s file system (-69766)”

I did some research and found an article on Tonymacx86.com about this issue and someone recommended running this command in terminal to fix the EFI issue.

See article:

https://www.tonymacx86.com/threads/the-p...

Sudo fsck_msdos disk0s1

I ran this and low and behold, no more errors in disk utility!

The computer seems to boot up fine when powered on, however , it was never a consistent issue so I am nervous it will come back at some points.

Additionally, when I go into System Preferences and open Startup Disk, it shows my 1 and only startup drive (the SSD), but when I select it and hit “restart” I get the Prohibitory Symbol?

I have already tried backing up the computer and doing a fresh install of macOS then restoring from backup.

IMHO something seems wrong with the OS and from time to time the computer is thinking that this version of MacOS is not compatible with this hardware or such?

So, I decided this morning to go into Recovery Mode and reinstall MacOS directly from there again, now that I have run that command in terminal to fix the EFI partition.  However, when I boot into recovery and start process of installation, I get to the screen where it asks where I want to install the new OS, and it doesn’t show the internal SSD.  It also doesn’t show the SSD in disk utility.

For some reason, this computer is not detecting the internal SSD, however it can boot from it, sometimes.

I am fully and utterly dumbfungled, so….

Any thought or ideas would be much appropriated as I want to get this computer running properly.

Thanks in advance form Mexico 🇲🇽!!

-Milo

@danj (tagging you because you’ve been so helpful in the past).