Windows 10 - 0xC0000021a

The issue can be caused by hardware such as hard drive or cabling issues among many.

Troubleshoot blue screen errors
http://windows.microsoft.com/en-us/windows-10/troubleshoot-blue-screen-errors 

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STOP: 0xC000021A

Can be a difficult problem to solve and you may indeed need technical help from a real computer shop (one that does its own in-house service) or the System Maker's Support.

Bug Check 0xC000021A: STATUS_SYSTEM_PROCESS_TERMINATED

The STATUS_SYSTEM_PROCESS_TERMINATED bug check has a value of 0xC000021A. This means that an error has occurred in a crucial user-mode subsystem.

Important Info If You Have Received a STOP Code

If you received a blue screen error, or stop code, the computer has shut down abruptly to protect itself from data loss. A hardware device, its driver, or related software might have caused this error.

If your copy of Windows came with your computer, call the manufacturer of your computer. If you purchased Windows separately from your computer, Microsoft provides support. To find contact info for Microsoft or your computer manufacturer, Contact Support.

If you have experience with computers and want to try to recover from this error, follow the steps provided in the Microsoft article Resolving STOP (Blue Screen) Errors in Windows.

These actions might prevent an error like this from happening again:

1. Download and install updates and device drivers for your computer from Windows Update.
2. Scan your computer for computer viruses.
3. Check your hard disk for errors.

STATUS_SYSTEM_PROCESS_TERMINATED Parameters

The following parameters are displayed on the blue screen.

Cause

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.

Resolution

Running the kernel debugger is not useful in this situation because the actual error occurred in a user-mode process.

Resolving an error in a user-mode device driver, system service, or third-party application: Because bug check 0xC000021A occurs in a user-mode process, the most common culprits are third-party applications. If the error occurred after the installation of a new or updated device driver, system service, or third-party application, the new software should be removed or disabled. Contact the manufacturer of the software about a possible update.

If the error occurs during system startup, restart your computer, and press F8 at the character-based menu that displays the operating system choices. At the resulting Windows Advanced Options menu, choose the Last Known Good Configuration option. This option is most effective when only one driver or service is added at a time. If this does not resolve the error, try manually removing the offending software. If the system partition is formatted with file allocation table (FAT), use an MS-DOS startup disk to gain access to the computer's hard disk. If the system partition is formatted with NTFS file system, you might be able to use Safe Mode to rename or delete the faulty software.

If the faulty software is used as part of the system startup process in Safe Mode, you need to start the computer using the Recovery Console in order to access the file. If a newly installed piece if hardware is suspected, remove it to see if this resolves the issue.

Try running the Emergency Recovery Disk (ERD) and allow the system to repair any errors that it detects.

Resolving a mismatched system file problem: If you have recently restored your hard disk from a backup, check if there is an updated version of the Backup/Restore program available from the manufacturer. Make sure the latest Windows Service Pack is installed.

STOP: 0xC000021A <-- read this link
http://www.faultwire.com/solutions-fatal_error/STATUS-SYSTEM-PROCESS-TERMINATED-0xC000021A-*1314.html

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would need to make a bootable USB or DVD using the Media Creation
Tool or other options.

How to Boot to Advanced Startup Options in Windows 10
http://www.tenforums.com/tutorials/2294-advanced-startup-options-boot-windows-10-a.html

Installing Windows 10 using the media creation tool - create media then
boot with it.
http://windows.microsoft.com/en-us/windows-10/media-creation-tool-install

Windows 10 includes special methods to Refresh (keep files and settings)  or a 
Reset (new install removing all).

How to Reset Windows 10

http://www.tenforums.com/tutorials/4130-reset-windows-10-a.html

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You may need to thoroughly check the hard drive for errors (be sure to inspect the cable as best you can).

Be sure to check for RootKits which can survive a format and installation of Windows.

TDSSKiller.exe. - Download to the Desktop - then go to it and Right Click on it - RUN AS ADMIN - it will show any infections in the report after running - if it will not run change the name from tdsskiller.exe to tdsskiller.com. Whether it finds anything or not does not mean you should not
check with the other methods below.
http://support.kaspersky.com/viruses/solutions?qid=208280684

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After checking the drive for RootKits inspect the drive and cabling. Then thoroughly
check the hard drive for errors using the Advanced Methods and the Manufactuter's  Diagnostic Utilities.

These are much more efficient methods to check the disk. <- Advanced Methods.

From the Command Prompt of the Windows 10 disk (boot from it) :

chkdsk /f /r
(Space after k and before /  and after f and before / )

REBOOT

sfc /scannow
(Space after c and before / )

REBOOT

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For even more thorough checking : <-- Manufacturer's Diagnostic Utilities.

(The old 302602 links is not valid now for the diagnostic links.)

Diagnostic Utilities By Manufacturer - run the one for your hard drive
http://www.techsupportforum.com/hardware-support/hard-drive-support/462298-no-ide-device-found.html

Corrected list as of 6-09-2010

Fujitsu Hard Drives: Diagnostic Utilities Here
http://www.fujitsu.com/emea/products/hdd/ 

Hitachi Hard Drives: Diagnostic Utilities Here
http://www.hitachigst.com/support/downloads/ 

IBM Hard Drives: Use Hitachi Utilities

Toshiba Hard Drives: Use Hitachi or Maxtor Utilities

Maxtor Hard Drives: Diagnostic Utilities Here (now SeaGate)
http://www.seagate.com/www/en-us/support/ 

Quantum Hard Drives: Use Maxtor Utilities

Seagate Hard Drives: Diagnostic Utilities Here
http://www.seagate.com/www/en-us/support/downloads 

Conner Hard Drives: Use Seagate Utilities 

Samsung Hard Drives: Diagnostic Utilities Here
http://www.samsung.com/global/business/hdd/ 

Western Digital Hard Drives: Diagnostic Utilities Here
http://support.wdc.com/product/download.asp?lang=en 

The trial versions of one of these "might" help.

SpeedFan
http://www.almico.com/sfdownload.php 

HD Tune
http://www.hdtune.com/