Bug Check 0xC000021A: STATUS_SYSTEM_PROCESS_TERMINATED
This error occurs when a user-mode subsystem, such as WinLogon or the Client Server Run-Time Subsystem (CSRSS), has been fatally compromised and security can no longer be guaranteed. In response, the operating system switches to kernel mode. Microsoft Windows cannot run without WinLogon or CSRSS. Therefore, this is one of the few cases where the failure of a user-mode service can shut down the system.
Mismatched system files can also cause this error. This can occur if you have restored your hard disk from a backup. Some backup programs might skip restoring system files that they determine are in use.
From Windows Recovery Environment choose Troubleshoot-> Advanced Options -> Advanced Options. pen the Command Prompt and type below command to repair any damage system files.
SFC /SCANNOW /OFFBOOTDIR=d:\ /OFFWINDIR=d:\windows
Replace the D: drive letter with Windows 10 installed partition letter.
When computer boots into WinRE environment the drive letter assign to Windows partition may not be C: drive letter because Windows 7, 8 , 8.1 and 10 creates a separate system partition when it's installed from scratch. The system partition contains boot files WinRE assigns the system partition the C: drive letter and the Windows installed partition will be assign any other drive letter usually D: drive letter is assign to Windows installed partition. The Bcdedit /enum | find "osdevice" command can be use to find out the drive letter of the Windows installed partition the output of the Bcdedit command is similar to this osdevice partition=D:. The drive letter after partition= is the drive letter of the Windows partition.