Answer to: Hard Drive not recognized by system during boot or installThis is the exact problem my son's friend had with his MBP. An Apple Tech acquaintance suggested it was the hard drive, but since I could Target Disk Mode his files to my Mac Mini, I really didn't think so. I changed it anyway, with no luck. I did a lot of googling, and decided it was the hard drive cable. Used the excellent help found here, and installed a new one. It works!