If the Windows drive or the firmware has been corrupted, then it can lead to this problem.
It can also happen if the hard disk has been corrupted, missing, or its connection is loose.
Some changes in the BIOS settings or missing Boot Configuration Data (BCD) can also cause this problem.
A corrupt Master Boot Record (MBR) can also be a reason behind this.
It mostly happens when the bootloader or the essential booting files are gone missing.
The following reasons can cause the Windows preparing automatic repair black screen. Instead, it displays a black screen or later restarts the automatic repairing (on a loop). In this, the system doesn't respond or boot correctly. Ideally, users can get the black screen after automatic repair due to different reasons. Part 1: Windows 10 Preparing Automatic Repair Black Screen: What's the Problem?
Part 3: How to Recover Lost Data after Fixing the Windows Black Screen Error?.
Part 2: How Do I Fix a Black Screen after Preparing Automatic Repair?.
Part 1: Windows 10 Preparing Automatic Repair Black Screen: What's the Problem?.