Issue with MacBook on Boot
You might be experiencing an HDD cable failure.  I've had to replace a few of them from 2009-2012 laptops.  They run about $40CAD on Amazon; you'll need your exact model number to find a compatible one.  To find that, hold option, and go to Apple > System Information.  Look for the Model ID, it'll be something like


  MacBookPro11,2


Good luck!