0xC000021A – Windows does not start correctly

A critical Windows process has terminated.

Record the stop code. Avoid speculative repairs after repeated crashes or drive errors. Contact IT for work computers.

Note stop code and last changes.
If accessible: at the login screen, press and hold Shift → Power → Restart → Troubleshoot → Advanced options. Have BitLocker key ready.
If the error occurs immediately after an update, “Uninstall updates” may be an option. Don't randomly remove updates; If you are unsure, ask for professional help.
Back up data or consult a data recovery professional before resetting or reinstalling. No installation over important unsecured files.

Test after each step and stop when the issue is solved. Checkmarks are not permanently saved.