Windows Defender Not Working? 10 Quick Fixes

Quick Fix

Open Windows Security app and check if protection is turned on. Click Start, type “Windows Security”, open it, and ensure all protection areas show green checkmarks. If you see warnings, click them to enable protection.

Understanding the Windows Defender Not Working Issue

Windows Defender (now called Microsoft Defender) is built-in antivirus protection for Windows 10 and 11. When it stops working, your PC becomes vulnerable to malware, viruses, and other threats.

Common signs include the Defender icon disappearing from the system tray, scan failures, real-time protection turning off automatically, or error messages when trying to access Windows Security. Third-party antivirus software can also conflict with Defender.

This guide helps restore Windows Defender functionality on Windows 10 and Windows 11.

Method 1: Enable Real-Time Protection

1. Press Windows + I to open Settings
2. Go to Privacy & security > Windows Security
3. Click Virus & threat protection
4. Under Virus & threat protection settings, click Manage settings
5. Toggle on Real-time protection

Method 2: Remove Third-Party Antivirus

1. Third-party antivirus disables Windows Defender automatically
2. Open Settings > Apps > Installed apps
3. Find any antivirus software (Norton, McAfee, Avast, etc.)
4. Click the three dots and select Uninstall
5. Restart your computer – Defender should reactivate

Method 3: Start Windows Security Service

1. Press Windows + R, type services.msc, press Enter
2. Find Windows Security Service
3. Double-click it and set Startup type to Automatic
4. Click Start if the service isn’t running
5. Also check Security Center service is running

Method 4: Run SFC and DISM

1. Right-click Start and select Terminal (Admin)
2. Type sfc /scannow and press Enter
3. Wait for the scan to complete
4. Then run DISM /Online /Cleanup-Image /RestoreHealth
5. Restart your computer after repairs complete

Method 5: Update Windows

1. Open Settings > Windows Update
2. Click Check for updates
3. Install all available updates, especially security updates
4. Restart your computer
5. Windows Defender definitions are updated through Windows Update

Method 6: Reset Windows Security App

1. Open Settings > Apps > Installed apps
2. Search for Windows Security
3. Click the three dots and select Advanced options
4. Scroll down and click Reset
5. This resets the app without losing protection

Method 7: Check Group Policy Settings

1. Press Windows + R, type gpedit.msc, press Enter
2. Navigate to: Computer Configuration > Administrative Templates > Windows Components > Microsoft Defender Antivirus
3. Double-click Turn off Microsoft Defender Antivirus
4. Set it to Not Configured or Disabled
5. Click Apply and restart

Method 8: Check Registry Settings

1. Press Windows + R, type regedit, press Enter
2. Navigate to: HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender
3. If DisableAntiSpyware exists with value 1, double-click it
4. Change the value to 0 or delete the entry
5. Restart your computer

Preventing Future Issues

• Keep Windows updated to ensure Defender works properly
• Don’t install multiple antivirus programs simultaneously
• Avoid disabling Defender for software installations – use exclusions instead
• Run periodic full system scans
• Be cautious with system optimization tools that may disable security features

FAQ

Why does Windows Defender keep turning off?

A third-party antivirus, malware, or group policy setting may be disabling it. Check for other security software and scan for malware using an offline scanner.

Is Windows Defender good enough?

Yes, Windows Defender consistently scores well in independent tests and provides excellent protection for most users without needing third-party software.

Can I use Windows Defender with another antivirus?

Not recommended. Running two antivirus programs causes conflicts. Defender automatically disables itself when third-party antivirus is installed.

Why does Windows Defender use so much CPU?

This usually happens during a scan. You can schedule scans for off-hours in Windows Security > Virus & threat protection > Scan options.

How do I add exclusions to Windows Defender?

Go to Windows Security > Virus & threat protection > Manage settings > Add or remove exclusions. Add folders or files that trigger false positives.

What if nothing fixes Windows Defender?

Consider a Windows Reset (Settings > System > Recovery > Reset this PC) keeping your files, which reinstalls Windows and all system components.