SSD Wont work but will in another MacBook. Please help!

[coady_nanton]

About 3 weeks ago I installed a SSD in my MacBook and everything was working fine. Two days ago I started my MacBook and a circle with a line appeared meaning it couldn't find a file path of the OS, I was thinking the SSD corrupted so I installed a HDD where my optical bay is so I could try and pull the info off of the SSD. File error would pop up for every file, this made me think the SSD almost certainly corrupted. I went and got it swapped out at BestBuy and installed the new one and tried installing an OS. The same circle with the line through it popped up. I then installed a HDD in the same spot as the SSD to see if it could maybe be the cable but I could indeed install the same OS on that HDD and it worked fine. I decided to go to the apple store and they couldn't figure it out either. I decided to buy the same exact model second hand off a friend to see if the SSD would work in the new one. I installed the same OS onto the SSD in the MacBook I just bought and it worked fine! I tried taking the working SSD from my new Mac and put it in my "old Mac" and the error popped up again.

If someone can figure my problem out it would be greatly appreciated

Specs:

New MacBook (Current Parts)
MacBook Pro 13" (Mid 2012) (Mojave 10.14.6)
2.9GHz i7
16gb DDR3 Ram
500GB SSD Samsung 860 EVO

Old MacBook (Current parts)
MacBook Pro 13" (Mid 2012) (Mojave 10.14.6)
2.5GHZ i5
4gb DDR3 Ram
500GB HDD
1TB HD (Replaced Optical Drive)

 

[smbu2000]

Have you tried to purchase a new Sata cable for the MBP? The sata cables in those models are very flaky especially when upgraded with a SSD.

https://macspro.com/macbook-pro-hdd-cable-failure/

https://beetstech.com/blog/prevent-a1278-mid-2012-hard-drive-cable-failure

 

[Fishrrman]

Replace the hard drive ribbon cable.
It will probably then boot right up.
Go to ifixit.com to see what's involved (if you know how to replace the drive you know how to replace the cable) and get the part number.