MacBook not powering at all/booting to black screen after HDD replace

This series requires a bootable drive to be connected, as you swapped out the drive to a new one it doesn’t offer the needed OS files to boot from. So you do need to put back the orginal drive if it’s still working to then build a bootable external drive. Ideally a 32GB thumb drive being the easiest.

If the current drive is not workable you can create it from another Mac system. Just be careful as you need to use Catalina or older macOS.

As you also state the system has a black screen, was this system working from the start? You maybe going down the wrong path here. Often times when I see a black screen the backlight power has issues so the screen can’t light up. To see if that’s the case you can take a good flashlight aiming it in via the Apple Logo in the lid to offer some light. Are you able to see your desktop and its icons?

If that fails to work then you’ll need to disconnect the drive and test again to make sure the drive is not shorted out.

Let us know what you discover!