Partially-Failed Hard Drive
My laptop hard drive was loading to the login screen, but would crash/shutdown half way through login. After many failed attempts to fix the issue, I decided it would be more beneficial to upgrade my slowing machine.
The replacement of hardware is the easiest part. Reinstalling the OS and transferring the non-corrupted files is the time suck with projects like this. Take your time with the file transfer and don't rush through it.
Hopefully you had a recent backup of the valuable data in your hard drive. I have done a repair similar to this before, but this time I used the silicone drive enclosure to format the new drive and install the updated OS. After the OS is installed on the new drive, the setup computer will see that as the startup disk. Be sure to select the correct startup disk on the computer you are using for setup, and then eject the freshly installed drive. Install the new drive in the machine you are fixing.