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Windows Defender by default installed on your Windows Vista/7/8/10. This built-in anti-malware will protect your PC from any spyware, malware, virus, and other malicious software. And it's free. However, some users found sometimes the Windows Defender is turned off, and it's not working as expected. Many possibilities are causing the Windows Defender to disable and can't turn on even you already restart your PC.
Some possibilities that cause Windows Defender is turned off
- Your computer already installed another Antivirus.
By default Windows Defender disable itself when detecting another Antivirus or Security software installed on PC. - Check the Windows Defender, and Windows OS is up to date.
Make sure your Windows and Windows Defender has latest update. - Manual Uninstall third-party Security software.
Some security software such as McAfee and Norton will break your Windows Defender function. You need an official removal tool from Norton and McAfee to uninstall it safely. - Malware attack.
Do you get malware attacks recently or recover from the attack? If so, try download and use portable antivirus, and scan your PC from USB. - Checking the Windows Defender setting and make sure the options are on. You can turn it on or off from Settings > Update & Security > Windows Security > Virus & threat protection settings.
- Windows Defender Service is not Running
Check and make sure Windows Defender services running. Open Service Manager (Windows logo + R key) then type “services.msc.” Check status is Running, and the Startup type is Automatic. - Missing some dll files. (advanced user only)
When you try to turn on the service, but WdNisSvc and WinDefend keep stopping. Try re-register following dll files: wuaueng.dll, softpub.dll, wucltui.dll, initpki.dll, wintrust.dll, wuweb.dll, wups.dll, mssip32.dll, atl.dll.Open Command Prompt or WindowsPowerShell, then type “regsvr32 [dll-files]” then Enter.
Example: regsvr32 softpub.dll - Wrong Date and Time
Wrong set your date and time, causing your Windows Defender won't work, and you can't turn it on. If you have incorrect date and time, adjust the clock to the correct time. - The network behind a proxy.
For some reason, Windows Defender will not update the definitions if your connection behind the proxy. When the Windows Defender is not up to date, it will disable itself.
