Why can't I turn on Windows Defender virus protection?

Today I noticed that my Windows Defender virus protection was off. I've been through countless blog entries, articles, and forums but I can't find anything that makes a difference.

I'm running Windows 10, Version 1803 (OS Build 17134.345)

I don't have any other antivirus software installed.

Here's the warning in Control Panel's Security and Maintenance section:

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Clicking "Turn on now" brings up this blank Security Center window:

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Under "Virus & threat protection", if I click "Scan now" nothing happens. If I click "Run a new advanced scan", then "Custom scan", then "Scan now" it'll prompt me to select a directory, but nothing happens after that.

Group Policy Editor
Computer Configuration > Administrative Templates > Windows Components > Windows Defender Antivirus is still "Not configured"

HKLM/SOFTWARE/Microsoft/Windows Defender -> DisableAntiSpyware
HKLM/SOFTWARE/Microsoft/Windows Defender -> DisableAntiVirus

  • both set to 0

Command Prompt

  • DISM.exe /Online /Cleanup-image /Restorehealth didn't report any problems
  • sfc /scannow did find and repair corrupt system files, but after rebooting nothing has changed

The "Restart" option for Security Center is disabled:

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I went more than a week without a solution, but I was due for an upgrade anyway... New hard drive and fresh installation means the problem is gone even though it was never solved.

Unfortunately, I won't be able to test or accept an answer for this problem.

  • What does Event Viewer tell you? What build of Windows 10 are you running? – music2myear Nov 2 '18 at 22:58
  • @music2myear I'm using Windows 10 Version 1803, OS Build 17134.345. I haven't used Event Viewer much. Can you give me an example of what I should click on and what I should look for? – Vince Nov 2 '18 at 23:06
  • Event Viewer is Windows' log system. You should at least check the System and Application logs for events around the time Defender tries starting, or for events referencing Defender or its dependencies. – music2myear Nov 2 '18 at 23:28
  • @music2myear The Application log just shows The Windows Security Center Service has started. and the System log doesn't show anything that seems relevant. – Vince Nov 3 '18 at 1:21
  • Security Center is not Windows Defender. But because of how both are integrated deeply into the OS, the real problem is corruption or an error in the Windows OS itself, and you should be treating this as an OS error issue, and attempting to identify and repair the OS. Common ways to do this are to force a reinstall of the latest major release and roll-ups, run deep scans for hidden malware, do a "Refresh" on the OS. – music2myear Nov 5 '18 at 16:15

I had the same sort of symptoms. In the Windows Security Center, under Virus and threat protection, it said "Your virus & threat protection is managed by your organization."

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I note you mentioned the Registry Keys under HKLM/SOFTWARE/Microsoft/Windows Defender. Nice spotting, but it seems like there is another key that is causing the problem for some users.

Steps to a solution:

  1. Press the Windows key and type "regedit"
  2. On the regedit icon that appears, right-click and select Run as Administrator.
  3. Navigate to the folder located at HKLM\SOFTWARE\Policies\Microsoft\Windows Defender (You can paste this into the address box at the top of the window, or navigate manually using the side directory structure)
  4. In this folder, there are probably two keys. Right-click and Delete the DisableAntiSpyware key.
  5. Exit regedit, and return to the Windows Defender settings screen (refresh it if necessary). Windows Defender should have the scan options available and working.

Solution adapted from here, with a much more detailed solution here.

  • 1
    I ended up buying a new hard drive and doing a fresh install, but I don't think your solution was related to my problem anyway. It didn't say "Your Virus & threat protection is managed by your organization". On my system, the "Virus & threat protection" view was blank just like "Home" and the registry key you mentioned was just another way to access the setting I had already checked within the Group Policy Editor. – Vince Nov 12 '18 at 14:30

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