Start with the right checks.
A failed download and a computer stuck while restarting are different situations. Begin by identifying which stage failed. That information helps avoid applying a repair intended for a different problem.
What to do next.
If Windows starts normally, open Settings, Windows Update and review the failed update and error code. Record its name and when it failed.
Check the power connection and whether ordinary websites load. Look for a pending restart and any storage warning.
Open Microsoft’s Windows Update troubleshooter through the Get Help app and follow the prompts that match your issue.
Try the offered update again after the recommended normal restart. Change one thing at a time and retain the original error information.
Check the result.
Check Windows Update after restarting and confirm whether the same update still fails. An empty error dialog is not proof that the update installed.
Stop and get help if…
The computer no longer starts, the same failure returns or a proposed fix asks you to disable protection or delete system folders. Get help with the recorded error before trying command line repairs from an unfamiliar website.