Windows 10: windows 10 anti virus defender is installed but am unable to use it ?

have had windows 10 for a number of years and the defender anti virus has in the last few days decided not to let me use it

can't understand why ?

:)

 

Anti Virus Problems

You should not be using more than one anti-vrus program on your computer. Read the
IMPORTANT NOTE about not using more than one anti-virus program in this

topic.

The inability to turn on Windows Defender 8/10 is typically the result of having a third-party anti-virus installed or failure to remove it properly (completely). Since Windows 8/10 Defender includes anti-virus protection, it is
disabled during the installation of another anti-virus program. If a trial anti-virus (i.e. McAfee, Norton, etc) came
preinstalled on your computer or you installed one, Windows Defender will be turned off (disabled). Windows Defender recognizes the install and automatically disables itself when other anti-virus products are used
to avoid conflicts. Windows Defender will remain disabled until that anti-virus software has been completely uninstalled. In some cases, you may need to download and run the anti-virus vendor's clean up tool to remove any remaining
remnants.

• Replacing your Anti-virus - List of Antivirus Uninstallers and Removal Tools
• Microsoft Wiki: List of anti-malware product removal tools by Stephen Boots,
  MVP

After removal of the third party anti-virus, Windows 8/10 Defender needs to be
activated if you choose to use it. When uninstalling the third-party anti-virus Defender should automatically turn itself on but sometimes you may receive a message indicating
your system has no protection...click here to turn on Windows Defender. If not, and Defender remains disabled, you will need to manually turn it on.

• How to turn Windows Defender On or Off in Windows 10
• How to turn Windows Defender On or Off in Windows 8

 

Can't activate Windows Defender. Message that there is an anti-virus program installed.

I've tried to activate Windows Defender real-time protection but I get a message that I already have an anti-virus program installed. I've gone to the Apps and Features option to verify that I have an anti-virus program installed and can't find an program
in the list. I did have Norton Anti-virus installed on this machine before I upgraded to Windows 10. Is it possible the program uninstall was incomplete and let some remnant that the system is seeing and thinks it is still installed?

Moved from Windows 10

Original title: Window 10 and Anti-virus

 

How to turn on Window Defender virus protection.

I installed Malwarebytes Anti-Malware. Now my Windows Defender is turned off. I need the virus protection but am unable to turn on Defender virus protection. I am using Windows 10. Any suggestions?