PC Error 0xc000021a: Your PC Ran Into a Problem at Sign-In
In plain English: Error 0xc000021a means a vital Windows sign-in process has stopped, so your PC halts before it can reach the desktop. Restarting usually brings back the same screen.
First safe step: Hold down the Shift key, select the Power icon in the lower right corner, then select Restart. Keep holding Shift until a blue screen titled Choose an option appears.
Error 0xc000021a means a vital Windows sign-in process has stopped, so your PC halts before it can reach the desktop. Restarting usually brings back the same screen. Every fix in this guide starts in the Windows Recovery Environment, the built-in repair screen outside normal Windows.
The steps work in order, from the least hands-on checks first. You will try a one-time bypass of driver signature checking to test a recent driver, and, if needed, roll back the most recent Windows update from recovery.
You do not need to sign in, download software, or use a driver updater, and none of those could run here anyway. This error also does not mean your personal files are automatically lost. Work slowly, and restart once after each step to test it.
Part of the Windows Error Codes in Plain English: Look Up Any Code series, the pillar guide for this cluster.
What Error 0xc000021a Means, and Why Sign-In Never Finishes
Error 0xc000021a means Winlogon has stopped. Winlogon is the Windows process that handles sign-in, and it depends on other core parts of Windows to finish that job. If Winlogon or one of those parts fails, Windows stops rather than carry on in an unsafe state.
That is why sign-in never finishes. You may see the sign-in screen briefly, or the PC may restart and show the same error again. The desktop never loads, so there is no normal place to run a repair from.
This error often follows a recent change. Common triggers include a recent Windows update, a new driver that does not work with your PC, damaged system files, or a program or service installed just before the trouble began. Try to remember what changed just before the first failure. That timing is a useful clue.
Because the PC stops before the desktop, fixes that start on the desktop cannot be the starting point here. That includes downloads and driver updater tools. Work has to start outside normal Windows instead. The error by itself does not mean your photos and documents have been erased. They are still on the drive unless something else has damaged them.
How to Reach the Recovery Screen When Windows Won't Start
If you can see the sign-in screen, use this route first. Hold down the Shift key, select the Power icon in the lower right corner, then select Restart. Keep holding Shift until a blue screen titled Choose an option appears. That blue screen is the start of the Windows Recovery Environment. You do not need to sign in to use it.
If the PC stops before the sign-in screen, turn it on and watch for the Windows logo or spinning dots. Hold the power button to turn it off, then repeat this three times. On the next start, Automatic Repair should appear. Select Advanced options to continue. This can take a few minutes, so leave the PC plugged in.
From Choose an option, select Troubleshoot, then Advanced options. You will use this same Advanced options screen for every fix that follows. The four tools in this article are Startup Repair, System Restore, Startup Settings, and Uninstall Updates. You do not need the other options for now. If a tool restarts the PC, use one of the routes above to come back to this screen.
If a BitLocker recovery screen appears instead, stop there. Find your 48-digit recovery key first, using the steps in our BitLocker key guide, and enter it only on your own PC. Never guess the key, and this site will never ask you for it. Guessing will not get past the screen.
Start With Startup Repair and a Restore Point
From Troubleshoot > Advanced options, start with Startup Repair. This is the least hands-on tool here. Windows checks for problems that keep it from starting, tries a fix on its own, and reports what it found. You do not need to pick settings or remove anything yourself at this stage.
Let Startup Repair run until it finishes, even if the screen stays quiet for a while. Do not turn the PC off, hold down the power button, or unplug it during the check. When it is done, restart once and try signing in normally to see if Windows now reaches the desktop.
If the code returns, go back to Advanced options and select System Restore. Pick a restore point dated before the first 0xc000021a failure, if one is listed. Check the date carefully, then follow the prompts and let the restore finish before you try signing in again.
System Restore returns Windows settings to that earlier date. Programs and drivers added after the point are removed, so you may need to install them again later. It does not target personal files such as photos and documents. If no suitable point exists, or the code returns afterward, do not repeat the same tool. Move on to the next step.
Turn Off Driver Signature Checking for One Start Only
Turn off driver signature checking for one start only
Windows checks a driver before it trusts it. The signature is a digital identity check. It confirms who made the driver and that the file has not been changed. If a driver added just before this error has a damaged or unrecognized signature, that check can stop Windows before sign-in. This step is a test, not a repair. It asks whether Windows will start when the check is skipped once.
From Advanced options, use these steps:
- Select Startup Settings, then select Restart.
- Wait for the Startup Settings list to appear after the PC restarts.
- Press 7 or F7 to select Disable driver signature enforcement.
Windows will then try to start with the signature check turned off for this start only. Watch whether it reaches the sign-in screen. Do not choose any other item on the list.
This setting is temporary, and that limit matters. It lasts for one start only, does not repair the driver, and turns back on at the next normal restart. Never use this start to install an unsigned driver offered by a website, an ad, or a pop-up. Do not install any unsigned driver during this start. With the check off, Windows has less protection against a bad or altered driver.
If Windows reaches sign-in, use that start for one job only. Remove or roll back the driver or program added just before the error first appeared, then restart normally. If sign-in works on the normal restart, that recent item was likely the trigger. If 0xc000021a returns on either start, the signature check was not the sole cause. Do not repeat this option. Move on to the next step.
Roll Back the Most Recent Windows Update From Recovery
If the code still appears, return to Troubleshoot > Advanced options and select Uninstall Updates. Try Uninstall latest quality update first. A quality update is the smaller, regular monthly update, and it is the most likely update trigger. Before you confirm, write down any update date or KB number shown. A KB number starts with KB, followed by several numbers. You do not need the desktop for this step.
Windows may ask for an administrator password before the removal starts. Enter it only if you know it, and do not guess. Let the removal run to the end, and do not turn off or unplug the PC during it, even if it seems slow. When it finishes, restart the PC and try to sign in the normal way. If sign-in works, that update was likely involved.
Try Uninstall latest feature update only in limited cases. Use it if no quality update can be removed, if removing the quality update did not help, or if the error began right after a large version upgrade. A feature update is that larger upgrade, so removal is a bigger job and can take longer. Expect the same password prompt, and keep the PC plugged in throughout.
If Windows later offers the same update again and 0xc000021a returns after it installs, compare the date or KB number with your note. A match points to that update as the likely trigger, so keep the note with the PC. Do not keep removing and reinstalling the same update in a loop. If sign-in still fails after the removals, do not repeat them. Move on to the next steps.
If the Recovery Fixes Don't Work: Safer Next Steps Before Reset
If you have tried Startup Repair, System Restore, the one-time driver signature start, and update removal, and 0xc000021a still returns, stop and do not run them again. Repeating a tool that already failed rarely changes the result, and each restart adds time without fixing the cause. Write down which steps you tried so anyone who helps you later does not have to start over.
The next option is to start the PC from recovery or Windows installation media made on another working PC, using instructions from Microsoft or the PC maker. Only after that should you consider Reset This PC, as a last resort. A reset removes installed programs and settings, and it can put personal files at risk. Read the full Reset This PC guide first.
Get in-person help instead if any of these apply. You cannot find the 48-digit BitLocker recovery key, you do not have the administrator password, the drive clicks or grinds or does not appear, or the PC belongs to work or school. Do not guess keys or passwords, force a failing drive, or pay for unsolicited remote support.
Once the PC starts again, write down what changed just before the first failure and what fixed it. Save your BitLocker recovery key somewhere safe away from the PC. Then make a fresh restore point and back up your files, and repeat both before you install a new driver or a major update. That record can save a lot of guesswork if the code returns.
Frequently asked questions
Can I fix error 0xc000021a after I sign in to Windows?
No, not as a first step. Windows stops before the desktop loads, so start in the Windows Recovery Environment and work from there.
Do the recovery steps in this article delete my photos and documents?
Startup Repair, System Restore, and uninstalling an update do not target personal files. Reset This PC is different, so treat it as a last resort and read its warning screens in full before you choose it.
If turning off driver signature checking works, can I keep it off?
No. That setting lasts for one start only and turns back on at the next normal restart. Use that start to remove or roll back the recent driver or program, then restart normally.
Conclusion
Error 0xc000021a looks final because the same screen keeps coming back, but the loop itself is a clue. Windows is stopping at the same early point each time, before sign-in finishes. Working from recovery, in order, lets you test that point without guesswork, downloads, or permanent changes you did not choose.
If none of the recovery steps got you back in, that result still narrows the problem. It points away from a simple recent driver or update and toward help, recovery media, or a last resort decision made with eyes open. Stop at that point rather than trying one more unknown tool.