Replacing broken hard drive cable
I use a dual SSD+HDD setup in my mid-2012 MBP. I keep the SSD in the optical drive adapter and the HDD in the stock hard drive space. My SSD contains the OS along with all of my applications, and my HDD contains my user files, some cache, and backups.
One day, every application that relied on my user data that was on my HDD just abruptly crashed: iTunes, Firefox, Spotify, MailMate, etc. I checked Finder to see that my HDD was not there anymore, and Disk Utility presented the same result.
There was not much I could do, so I just restarted the computer since I wasn't too sure what happened. However, when I tried to log back in, I received a message that said that my user account was unavailable. Of course, this makes sense with hindsight because my HDD contained my user account data and the hard drive cable suddenly broke.
Because my SSD was still functional, I decided to reinstall my OS in recovery mode such that the user account data would be located on the SDD so that I could log in and begin to troubleshoot. I was worried that my HDD failed, but upon removing my HDD and connecting it via USB with an external hard drive enclosure, I was relieved that all my HDD files were still present. I tested a spare HDD I had in the hard drive bay of the computer to make sure, and it wasn't recognized. From this, I concluded that the hard drive cable must have been at fault. I actually tried flexing the cable and reconnecting everything; I was able to read my HDD for a couple of hours, but the connection failed afterwards.
At that point, I went here to buy a replacement cable for about $45, which beats buying a new laptop.
It's was pretty easy for me. With the proper tools, you can do it in half and hour. Of course, take care to disconnect the battery from the logic board.
With my particular hard drive setup, I would have created a guest account before I restarted my computer to find that I couldn't log in. The guest account would be local to the SSD, so I would've been able to log in and I wouldn't have had to reinstall the OS in recovery mode. The drudgery was not in the repair, but in migrating my user data back with the Migration Assistant. This probably took 1-2 hours.