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Boot and recovery fix • Windows • Step-by-step Windows help

Fix Error 0xc000021a after sign-in or during boot

This guide is for critical logon process failure, updates, and recovery startup. It explains the fast repair path first so the user can test the common fixes before going deeper.

Overview

What this guide helps you do

Boot and recovery pages get copied badly online. A better guide should separate the first checks from the deeper recovery steps so the user does not jump straight into risky changes.

  • This page is focused on Error 0xc000021a after sign-in or during boot, not on random generic cleanup tips.
  • The fastest path is usually a repair-command pass plus one or two targeted checks.
  • If the same code returns after every restart, check drivers, recent changes, and system integrity before reinstalling Windows.

When to use this

When to use this guide

Best when the same problem or code keeps returning after a restart, app relaunch, or normal retry attempt.

Before you start

What to review first

Do not stack many repair changes at once. Test one stage, check the result, and then continue only if the error remains.

Do this exactly

Open the right Windows area first, then follow the changes one by one

  1. Open Windows Terminal or Command Prompt as administrator.
  2. Run sfc /scannow and wait for the result.
  3. Run DISM /Online /Cleanup-Image /RestoreHealth after SFC finishes.
  4. Restart the PC and test the exact error again.
  5. If the issue remains, continue with the focused checks below for this specific problem.

Exact click path

Tell the user exactly what to open and press

Do not change ten things at once. Open the exact Windows page first, make one clear change, then check whether it solved the problem before moving on.

Fast open: Start with Windows Terminal as administrator, run SFC and DISM, then follow the problem-specific checks below.

Try a faster path

Best when the same problem or code keeps returning after a restart, app relaunch, or normal retry attempt.

PowerShell Clean Up PC Script Windows Update Reset Helper

How to use

Do not stack many repair changes at once. Test one stage, check the result, and then continue only if the error remains.

Related pages

Keep going with the next useful page

Use these links when you want the matching script, another Windows help page, or a browser tool for the same job.

Open the tools section Browse all script pages Open the Windows section How to Stop Windows from Tracking Activity How to Disable Telemetry Safely How to Remove Personal Metadata from Files Before Sharing

FAQ

Questions about Fix Error 0xc000021a after sign-in or during boot

Can this usually be fixed without reinstalling Windows?

Yes, many cases can be fixed with repair commands, update cleanup, runtime reinstall, or startup recovery before a full reinstall is needed.

How long does this fix take?

Most fixes take 10 to 30 minutes, but deeper checks such as recovery startup, app reinstall, or driver work can take longer.