Error 0xc000021a — the sign-in crash, explained and fixed

0xc000021a (STATUS_SYSTEM_PROCESS_TERMINATED) means one of two processes Windows cannot sign you in without — Winlogon or CSRSS — stopped. The PC typically loops: boot, blue screen, restart. Because it happens before sign-in, the fixes run from the recovery environment, and the leading cause is a recent update landing badly.

The fix, in order

  1. Get to the recovery menu: interrupt startup twice (power off as Windows starts loading) or boot a Windows USB → Troubleshoot → Advanced options.
  2. Uninstall the latest quality update (Advanced options → Uninstall Updates). This is the fix in most modern cases.
  3. Run System Restore to a point before the crashes, if one exists.
  4. Repair system files offline: from the recovery Command Prompt, run sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows (drive letter may differ — check with dir on likely letters).
  5. If you recently installed security or system software, use Safe Mode from Startup Settings and uninstall it — programs that hook the sign-in chain can kill Winlogon.

If it still happens

If none of the recovery options work, “Reset this PC → Keep my files” from the recovery menu rebuilds Windows while preserving your data. If even the reset fails, suspect the drive itself and prioritise copying files off it with a bootable USB.

Common questions

What is Winlogon, in plain terms? The process that runs the sign-in screen and starts your session. If it dies, Windows has no safe way to hand you the desktop — so it stops with this code instead.

Is 0xc000021a caused by a virus? Rarely. Damaged or replaced system files are the usual story, and a bad update is the most common way they get that way.

Related errors

CRITICAL_PROCESS_DIED · INACCESSIBLE_BOOT_DEVICE · Windows Update error 0x80070002