Оригинальный сообщение: Dan ,
You'll need to create a OS installer drive from your friends Mac. Here's how: [https://www.macworld.com/article/3092900/macs/how-to-create-a-bootable-macos-sierra-installer-drive.html|How to create a bootable macOS Sierra installer drive] Independent of creating the installer you'll need to replace the HD SATA cable as I doubt your SSD went South on its own. In fact I wouldn't be surprised if after replacing the cable your system startup up! Here's the IFIXIT guide: [guide|1716] The newer version of this cabe (2012 model) is a better cable I would recommend putting it in. Here's the part: [product|IF161-100-4] The reason this happens is the rough surface of the aluminum uppercase wears the cable. Even still I recommend you apply electricians tape on the upper case where the cabe rests to offer additional protection and don't over bend the folds! Once you get the cable replaced see it the system boots up on its own. If it does you really want to make a backup ASAP! (TimeMachine). Then using the OS installer drive reformat the drive and install a fresh copy of MacOS, then restore your backup that way your files are safe.