Fixing Windows Error 0xc000021a: Causes, Step-by-Step Fixes, and Expert Tricks

 Is Your PC Stuck in a Reboot Loop with Error Code 0xc000021a?

You’re not alone.

Many users report suddenly seeing the error message:

“Your PC ran into a problem and needs to restart. Error Code: 0xc000021a”

…and from there, the system gets stuck in a restart loop, never even reaching the login screen. This is one of Windows’ most critical failures—often triggered by broken system files or failed updates.

But don’t panic. This guide walks you through easy-to-follow solutions, advanced fixes, and hidden tricks to recover your PC—without needing to be a tech expert.

What Is Error Code 0xc000021a?

This error occurs when critical system processes like winlogon.exe (Windows Logon Process) or csrss.exe (Client Server Runtime Subsystem) unexpectedly terminate. These are core processes required for Windows to start. If they stop functioning, the entire system crashes.

Common Causes Behind the Error

Here’s what typically triggers this issue:

• Failed Windows Updates — especially after reboot
• Corrupted system files like DLLs or registry entries
• Faulty third-party drivers
• External devices like USB drives interfering with the boot process
• Antivirus software that mistakenly quarantines system files

Even outdated drivers or misbehaving peripherals can prevent Windows from starting. The exact cause is often unclear, but by going through the steps below, you’ll likely fix the issue.

Basic Fixes to Try First

These steps are designed for anyone to follow—even if you can’t log in to Windows.

Step 1: Disconnect All External Devices

Remove all USB drives, printers, or external hard drives. Then, restart your PC and check if the error disappears.

Step 2: Boot into Safe Mode

1. Force shut down your PC by holding the power button (repeat 3 times).
2. When the “Automatic Repair” screen appears, choose Advanced Options.
3. Go to Troubleshoot > Startup Settings > Restart.
4. From the menu, press 4 to boot into Safe Mode.

If Safe Mode works, you can proceed with repairs.

Step 3: Repair System Files via Command Prompt

Open Command Prompt via Safe Mode or Recovery Tools and run:

This will check for and fix any corrupted system files.

Step 4: Use System Restore

If you’ve previously created a restore point:

• Go to Advanced Options > System Restore
• Choose a restore point before the problem began and follow the prompts.

Step 5: Try Startup Repair

From the same recovery screen:

• Go to Advanced Options > Startup Repair
• Windows will attempt to find and fix boot-related issues automatically.

Expert Techniques (Advanced Users Only)

Trick 1: Rebuild the Boot Configuration Data (BCD)

If the boot sector is damaged, use these commands:

📌 You’ll need a recovery drive or Windows installation USB to access Command Prompt from the Repair screen.

＊After executing each command, check for messages like “Operation completed successfully.”

These commands are effective if the root issue lies in boot records or the Master Boot Record (MBR).

⚠️ Be cautious…mistakes here could corrupt your boot setup further. Follow each step precisely.

Trick 2: Uninstall Faulty Third-Party Drivers

If Safe Mode works, open Device Manager and uninstall any unfamiliar or recently installed drivers that might be interfering.

Trick 3: Use Legacy Hotkeys to Enter Recovery Mode

On older PCs, pressing F11 or Shift + F8 repeatedly during startup may open WinRE (Windows Recovery Environment).

Note: This no longer works reliably on newer devices with fast boot enabled.

Frequently Asked Questions (FAQ)

Last Resort: Reinstalling Windows

If all else fails, you may need to reinstall Windows:

• Reset this PC (Keep files, remove apps)
  Go to Settings > Recovery > Reset this PC
  This option reinstalls Windows while keeping personal files.
• Clean Install via USB
  Download the Media Creation Tool from Microsoft and prepare a bootable USB.

💡 Backup important data first using external drives or OneDrive, if possible.

Summary

Error 0xc000021a may feel like the end of the road—but it isn’t.

With the right steps, most users can fix this issue without professional help.

• Start with Safe Mode and system repair tools.
• Use advanced methods cautiously.
• If needed, reset or reinstall Windows—but always back up your data first.

Stay calm and follow this guide step by step—you can do it.

✔️Looking for more tips? Try these

▶︎How to Fix Windows Error 0x800F0954 When Installing .NET Framework

▶︎Troubleshooting Windows 11 Update Error KB5054979 (June 2025)

▶︎How to Disable or Remap the CapsLock Key on Windows: Simple and Safe Methods

タグ: Windows error, bootrec, 0xc000021a, BCD repair, safe mode, Reboot loop, Windows boot issue, Windows recovery