Unable to turn on Windows Defender in Windows 7/8/10

When I browse through forums I often find this question asked many times – I am unable to turn on Windows Defender in Windows 7 or Windows 8, or Windows Defender wont or will not turn on and start. In this post I’ll list some common issues that can affect Windows Defender.

Unable to turn on Windows Defender

Windows Defender

Scenario 1:

On of the most common behavior of Windows Defender is that if it detects a third-party antivirus software, then Windows Defender will shut itself off. Windows is designed to detect the presence of security software installed, and we often we get to see the notification in the Action Center. One of the common issues we have seen in the past, is when there are multiple security software installed. It often creates a conflict between them and in the end, in creates more trouble than doing any good. Frequent freezing, crashing to applications are some of the common issues which occur when you install more than one antivirus software.

So to avoid this situation Windows Defender will turn itself off when it detects another security program. Likewise if this security application has a Firewall then Windows Firewall will also stop working. So in case you want Windows Defender to work, then you will have to uninstall your third-party security software and reboot the system.

Often users maybe unaware if a security software is indeed installed or not because when you buy a new Laptop mostly it comes with a trial version of security software like Norton, McAfee etc. Then when you install applications like Flash or java it might prompt you to uninstall free security scanner when most of them won’t notice. So it’s best to search your PC if you’re not sure if a security software is installed or not. Once it’ removed you may need to manually turn it back on.

  • Press the Windows + Q key on the keyboard to bring up the charms search.
  • Type “Windows Defender” in the search box and then press enter.
  • Click Settings and make sure there is a check mark on Turn on real time protection recommend.

Scenario 2:

Then other issues than could cause Windows Defender to not work properly is incorrect date or time on your Windows 8 machine. Make sure you have set your Window clock & date set properly and then try to turn you Windows Defender back on and see if it works fine. It’s strange, but most of the Windows operating system functions work, based on the system date and time. So an incorrect date or time could trigger abnormal behavior in your Windows OS.

Scenario 3:

Another important thing that could cause issues is, if you Windows is not up to date, in terms of Windows Update. This could cause issues in Windows Defender or any other Windows core application. When it comes to any security software, it always needs the latest signature updates and other Windows core updates to keep your PC secure. So I would highly recommend to run a complete Windows Update, then go into Windows Defender and run an update from there as well. Then see if your Windows Defender is working fine.

Other Common Issues:

The above discussed scenarios are the most common ones. Apart from these, there could be some minor issues that could affect the working of Windows Defender. It could incorrect Zone setting in Internet Explorer, which you can fix by resetting Internet Explorer to factory settings. Again, if you are using a Proxy server, Windows Defender will not be able to update.

In such cases, you need to make some small changes to your Proxy server.

  • Press Windows + X and select Command Prompt (Admin)
  • Now reboot the System and see if it works.

Finally, it could a malware itself that’s causing Windows Defender to not to work properly. You could download and use Windows Defender Offline Tool or any other standalone antivirus software and run a complete scan.

These are some common reasons why Windows Defender does not start.

Windows Defender is turned off or not working offers some additional troubleshooting suggestions, which may also interest you.

You may want to also check out these posts which help troubleshoot Windows Defender problems:

  1. Error 0x800106a, Windows Defender will not turn on
  2. Windows Defender Error Code 0x800106ba : Application failed to initialize
  3. Windows Defender Error : MSASCui.exe – Unable To Locate Component.
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Shyam aka “Captain Jack” is a Microsoft MVP alumnus and a Windows Enthusiast with an interest in Advanced Windows troubleshooting. Suggestions made and opinions expressed by him here are his personal one's and not of his current employers. He blogs at captaindbg.com.