
Windows Defender Service Troubleshooting Checklist
If Windows Defender won't start, won't update, or shows error messages like "Service stopped" or ...
Software troubleshooting desk

If Windows Defender won't start, won't update, or shows error messages like "Service stopped" or ...

You open Windows Security and see a 404 Not Found error, or the app won't load at all. Often this...

When the Task Scheduler service stops working, scheduled tasks may not run, or the service itself...

When you run chkdsk from Command Prompt and see "Access Denied" or "You do not have ...

You've scheduled a task in Windows Task Scheduler, but when it runs, you see: Task Schedule...

If Windows Search stops working—no results, missing files, or high CPU usage—reinstalling the fea...