回答“MacBook Pro screen display stays black but works on external monitor.”With these models this can sometimes be caused by either a faulty LCD Cable or a faulty LCD. It runs from the LCD to the Logic board. I would recommend if you can and have the knowledge to replace it yourself or take it to a reputable repair shop for help with it. This sounds to be a hardware issue more so than a software issue unfortunatly
回答“MBP won't start after SSD install”Are you able to put in your old HD and Boot into it? Your Computer model is very notorious for having a bad GPU. Unfortunately there is not an easy fix for this without the use of Soldering or a replacement Motherboard. However, you would be running into the issue of the same problem happening again. Personally I would recommend looking into a replacement machine as the cost of repair for this computer vs. the value of it doesn’t make it worth the repair.