Full Fix: Windows Defender won’t turn on Windows 10, 8.1, 7

Madeleine Dean By: Madeleine Dean
7 minute read

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Many Windows 10 users are reporting they can’t turn on Windows Defender because Microsoft’s antimalware tool detects there is another antivirus software running, although users confirm they have uninstalled all third-party security software.

This isn’t the first time users have reported they cant’ turn on Windows Defender, but we can’t help but notice there has been an explosion of issues surrounding Windows 10’s built-in antivirus following the Anniversary Update release.

Fix: Windows Defender won’t turn on, how to fix it?

Windows Defender is a built-in antivirus in Windows 10, and it provides solid protection for the most part. However, many users reported that Windows Defender won’t turn on on their PC, and this could be a problem. Speaking of problems, these are some of the common issues that users reported:

  • Can’t turn on Windows Defender Windows 8 – This problem can also appear on Windows 8, but you should be able to fix it using one of our solutions.
  • Windows Defender won’t open – Many users claim that Windows Defender won’t open on their PC. If that’s the case, remove all third-party antivirus tools from your PC. In addition, be sure to remove all files and registry entries associated with your antivirus.
  • Windows Defender is turned off by group policy – Sometimes Windows Defender won’t run since it’s disabled from Group Policy. However, you can easily fix that with one of our solutions.
  • Windows Defender won’t turn on unexpected error – In some cases, you might get an error message while trying to start Windows Defender. If that happens, try performing SFC and DISM scans and check if that solves your issue.
  • Windows Defender won’t turn on after uninstalling Avast, Bitdefender, McAfee, AVG – Sometimes Windows Defender won’t start even after you uninstall your antivirus. To fix that issue, be sure to use the dedicated removal tool to remove all leftover files and registry entries associated with your antivirus.
  • Windows Defender won’t turn on Windows 10 Spybot – Many Windows 10 users reported this issue with Spybot application. To fix the issue, be sure to remove Spybot completely from your PC and check if that solves the problem.
  • Windows Defender won’t open, run, work, enable, start – There are many problems with Windows Defender that can occur, and if you have issues running Windows Defender, feel free to try some of our solutions.

Solution 1 – Use antivirus specific removal tools

When you uninstall third-party antivirus solutions using the Uninstall option from the Control Panel, it’s possible that some files remain undetected and this prevents you from running Windows Defender. Check out this list of antivirus removal tools, and run the tool available for the antivirus you used before installing Windows Defender.

In addition to these tools, you can also use uninstaller software to completely remove your antivirus from your PC. If you’re not familiar, uninstaller software is a special application optimized for removing programs.

The uninstaller will remove the selected application, but it will also remove all files and registry entries associated with that application. As a result, the selected application will be completely removed and it will be as if the application was never installed.

As for uninstaller software, there are many great tools, but the best are IOBit Uninstaller or Revo Uninstaller. All these tools are simple to use, so you should be able to remove your antivirus with ease.

Uninstall the remnants of your previous antivirus, restart your computer and Windows Defender should be automatically enabled.


Solution 2 – Check your system files

The System File Checker tool repairs corruption in system files. Use this tool to verify whether Windows Defender is corrupted or not. To perform an SFC scan, do the following:

  1. Press Windows Key + X to open Win + X menu. Now select Command Prompt (Admin) or PowerShell (Admin) from the menu.
    Windows Defender is turned off by group policy
  2. Type the command sfc /scannow > hit ENTER > wait for the scan to complete.
    Windows Defender won't turn on Windows 10 Spybot

If you can’t run SFC scan or if SFC can’t fix the problem, you might want to try using DISM scan instead. To do that, just follow these steps:

  1. Start Command Prompt as administrator.
  2. When Command Prompt opens, enter DISM /Online /Cleanup-Image /RestoreHealth and press Enter to run the command.
    Windows Defender won't turn on unexpected error
  3. DISM scan will now start. This scan can take up to 20 minutes or more, so don’t interrupt it.

Once the scan is finished, check if the problem still persists. If you were unable to run SFC scan before, or if DISM scan doesn’t solve your problem, repeat the SFC scan again and check if that solves the issue.


Solution 3 – Clean boot your computer

Sometimes third-party applications can interfere with Windows and cause this problem to appear. However, you can find the problematic application by performing a Clean boot. This is quite simple, and you can do it by following these steps:

  1. Press Windows Key + R and enter msconfig. Press Enter or click OK.
    Windows Defender won’t run
  2. System Configuration window will now appear. Go to Services tab and check Hide all Microsoft services. Now click the Disable all button.
    Can't turn on Windows Defender Windows 8
  3. Navigate to Startup tab and click Open Task Manager.
    Windows Defender won't open
  4. Now you’ll see a list of startup applications. Right-click the first entry on the list and choose Disable. Repeat this step for all startup applications.
    Can't turn on Windows Defender Windows 8

  5. For various PC problems, we recommend this tool.

    This software will repair common computer errors, protect you from file loss, malware, hardware failure and optimize your PC for maximum performance. Fix PC issues now in 3 easy steps:

    1. Download this PC Repair Tool rated "Excellent" on TrustPilot.com.
    2. Click “Start Scan” to find Windows issues that could be causing PC problems.
    3. Click “Repair All” to fix all issues with Patented Technologies (requires upgrade).

  6. Once you disable all startup applications, go back to System Configuration window and click Apply and OK. Now choose to restart your PC.
    Windows Defender won't open

Once your PC restarts, check if the problem still persists. It means that one of the disabled apps or services was causing the problem. To find the problematic app or service, you need to enable them one by one or in groups until you recreate the issue. Now disable or uninstall that application and the issue will be resolved.


Solution 4 – Restart the Security Center Service

In order for Windows Defender to work properly, you need to have certain services enabled. If those services aren’t running properly, Windows Defender won’t be able to turn on at all. However, you can always start the necessary services by doing the following:

  1. Press Windows key + R > launch Run. Type services.msc > hit Enter or click OK.
    Windows Defender won't turn on unexpected error
  2. In Services, search for Security Center. Right-click on Security Center > click on Restart.
    Windows Defender won't turn on after uninstalling Bitdefender

Once you restart the required services, check if the problem with Windows Defender is resolved.


Solution 5 – Change your group policy

Sometimes Windows Defender won’t turn on because it’s disabled by your group policy. This can be a problem, but you can fix it simply by changing that group policy. To do that, just follow these steps:

  1. Press Windows Key + R and enter gpedit.msc. Now press Enter or click OK.
    Windows Defender won't turn on after uninstalling Avast
  2. When Group Policy Editor opens, in the left pane navigate to Computer Configuration > Administrative Template > Windows Components > Windows Defender Antivirus. In the right pane, double click Turn off Windows Defender Antivirus.
    Windows Defender won't turn on Windows 10 Spybot
  3. Select Not Configured and click on Apply and OK to save changes.
    Windows Defender is turned off by group policy

After making these changes, Windows Defender should be enabled, and it will run without any problems on your PC.


Solution 6 – Modify your registry

If Windows Defender won’t turn on, the problem might be related to your registry. However, you can easily modify your registry and fix this issue by doing the following:

  1. Press Windows Key + R and enter regedit. Press Enter or click OK.
    Windows Defender won’t open
  2. When Registry Editor opens, navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender in the left pane. In the right pane, look for DisableAntiSpyware DWORD and double click it. If the DWORD isn’t available, right click the right pane and choose New > DWORD (32-bit) Value from the menu.
    Can't turn on Windows Defender Windows 8
  3. Set Value data to 0 and click OK to save changes.
    Windows Defender won't open

After doing that, Windows Defender should be enabled on your PC and it will start working without any problems.

If you’re an advanced user and you prefer using the command line, you can do this from Command Prompt or PowerShell by doing the following:

  1. Start Command Prompt as administrator.
  2. Now enter REG ADD “HKLM\SOFTWARE\Policies\Microsoft\Windows Defender” /v DisableAntiSpyware /t REG_DWORD /d 0 /f command and press Enter to run it.
    Windows Defender is turned off by group policy

After doing that, the selected DWORD will be instantly changed to 0 and the problem should be resolved.

Some users are also suggesting to delete DisableAntiSpyware DWORD, so you might want to try that as well.

If you’re still having issues on your PC or you simply want to avoid them for the future, we also recommend you to download this tool to fix various PC problems, such as file loss, malware and hardware failure. It will also optimize your PC for maximum performance.


Editor’s Note: This post was originally published in August 2016 and has been since completely revamped and updated for freshness, accuracy, and comprehensiveness.


RELATED STORIES YOU NEED TO CHECK OUT:

For various PC problems, we recommend this tool.

This software will repair common computer errors, protect you from file loss, malware, hardware failure and optimize your PC for maximum performance. Fix PC issues now in 3 easy steps:

  1. Download this PC Repair Tool rated "Excellent" on TrustPilot.com.
  2. Click “Start Scan” to find Windows issues that could be causing PC problems.
  3. Click “Repair All” to fix all issues with Patented Technologies (requires upgrade).

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