A known issue with the Mid-2012 13″ model Macbook Pro is that the internal HD cable can easily fail. This creates all sorts of problems that look a lot more serious than they are:
- Mac won’t boot.
- Mac boot screen gets stuck for a long time at various parts of the process.
- Mac very slow.
- Disk repair fsck utility fails in various ways.
- Various diagnostic tools will tell you your HDD (or my SSD!) had failed.
NB—if your MacBook Pro is still in warranty then use the warranty service first before you do anything below.
If your MacBook Pro is out of warranty, you can get a replacement cable for nearly a tenner (British money) including all the tools you need, and there are loads of videos or instructions online to help you replace it yourself.
Having had two of these cables fail on me, I have an extra tip: when you replace the cable, tape a small coin either side of the place where the HD cable bends (5p piece did the trick for me, but 1 or 2 cents in American money would also work). This creates a buffer to stop the base of the laptop pressing against the cable, which is what I think causes the fault.
The only disadvantage of this system is it’s slightly more restricted airflow within the MacBook; and mine is liable to overheat.