Hard Drive Issues with MacBook Pro 13-inch mid-2012
So, after buying a new SSHD and SATA cable, spending 3 weeks reading and writing command lines on Terminal.... this is what fixed my problem, believe it or not:
https://www.youtube.com/watch?v=Amg5w0rlwDo&amp;spfreload=10

This video shows how an electric tape can isolate the sata cable and prevent it to touch the aluminium surface, which will cause you some problems.

I mean, seriously Apple? The design of the SATA cable path is so prone to failure....it's obvious!