A stop code during startup leaves fewer safe checks available than a crash after sign-in. Confirm whether the PC reaches Windows RE or Safe Mode.
Protect your files first
Back up important files when possible. If the drive is encrypted, locate the BitLocker recovery key before recovery changes. Stop if storage appears to be failing or this is a work or school managed PC.
What to record
Exact stop code, stage of startup, drive detection, recent update or driver change, backup and BitLocker status.
The exact message, Windows version, and whether the desktop still opens matter more than a guess based on the symptom name.
Try these safer checks
If Windows RE opens, record the code and try Startup Repair only when the symptom is a startup failure. If Safe Mode works, use that result to review a recent driver change.
Change one thing at a time. After each check, see whether the same symptom returns and write down what changed.
When to stop and get help
A missing or unstable drive and unbacked-up files are reasons to stop before reset, reinstall, or boot-record changes.
If this is a work or school device, contact its administrator before changing managed settings.
Keep track of your checks
This checklist stays in this browser session. It is not sent to WinErrors.