I ran across my third MacBook Pro with a bad HD ribbon cable last week. There’s a thriving cottage industry selling replacement cables. The cable has multiple 90 degree bends that fail over time. The last MacBook needed cable model 821-1480-a. Make sure you get the right one for your Mac. iFixIt has excellent guides on replacing the cable. Their iFixIt Pro Tech Toolkit is a must-have for tearing apart Apple hardware and notebooks/tablets/phones/etc in general.