- Search for gpedit.msc on the home screen search box near the Start menu.
- Click to open the file. The Local Group Policy Editor window opens.
- Select Administrative Templates under Computer Configuration. Then click Windows Components and select Windows Defender from the list.
- Click Turn off Windows Defender and Disable it. Now, turn ON Windows Defender.
- If the issue persists, uninstall or remove other third-party firewalls and security programs.
- Restart Security Center from the Services section.
- Run an SFC scan in the command prompt window.
- Upgrade your operating system to the latest version.
- If Windows Defender still doesn’t turn ON, uninstall and reinstall it.