When you open Windows Defender, it may inform you that Windows Defender protection is not enabled in the computer. And, when trying to start the Windows Defender service via Services MMC, the following error may appear:
The Windows Defender Service service on Local Computer started and then stopped. Some services stop automatically if they are not in use by other services or programs.
This can happen if there is a third-party anti-virus software present in the system. It is possible that you installed a third-party anti-virus software earlier and disabled the appropriate services related to that software. To resolve this, uninstall the third-party anti-virus software completely so that Windows Defender can start successfully.
In some cases, the user needs to run a specialized uninstaller tool supplied by the anti-virus software manufacturer, even if the product was already uninstalled via Control Panel – Programs and Features.
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Ramesh Srinivasan founded Winhelponline.com back in 2005. He is passionate about Microsoft technologies and has a vast experience in the ITeS industry — delivering support for Microsoft's consumer products. He has been a Microsoft MVP [2003 to 2012] who contributes to various Windows support forums.