How to Fix Windows Defender Won't Turn On

Why Won't Windows Defender Turn On?

You click to enable Windows Defender, but nothing happens. Or maybe you see an error message saying it can't be turned on. This is frustrating because Windows Defender is your primary defense against viruses and malware—when it's not working, your PC is vulnerable.

Windows Defender (now called Microsoft Defender Antivirus) can fail to turn on for several reasons: conflicts with third-party antivirus software, corrupted system files, disabled Windows services, malware infections that have disabled it, or incorrect group policy settings. The good news is that most of these issues can be fixed without professional help.

Quick Fix: Enable Real-Time Protection

Sometimes Windows Defender appears off simply because Real-time protection is disabled. Here's the fastest fix:

1. Click Start and type "Windows Security" then open the app
2. Click "Virus & threat protection" in the left menu
3. Under "Virus & threat protection settings," click "Manage settings"
4. Toggle "Real-time protection" to On
5. Also enable "Cloud-delivered protection" and "Automatic sample submission"

If the toggle switches back to Off immediately, or you see an error like "This setting is managed by your administrator," continue to the detailed steps below.

Common Error Messages

You might see these messages when Windows Defender won't turn on:

• "This setting is managed by your administrator"
• "The service couldn't be started"
• "Virus protection is turned off"
• "Real-time protection is off. Your device is vulnerable."
• "Unexpected error. Sorry, we ran into a problem"

Complete Fix Steps

Step 1: Uninstall Third-Party Antivirus Software

The most common reason Windows Defender won't turn on is that you have another antivirus program installed. Windows automatically disables Defender when it detects third-party security software.

1. Press Windows key and go to Settings > Apps > Installed apps
2. Look for antivirus programs like Norton, McAfee, AVG, Avast, Kaspersky, etc.
3. Click the three dots next to the program and select "Uninstall"
4. Follow the uninstall wizard carefully—some antivirus programs leave behind components
5. Restart your computer after uninstalling
6. Try turning on Windows Defender again

If you prefer third-party antivirus, that's fine—but you can't run both simultaneously. If you want to use Windows Defender, all other antivirus software must be completely removed.

Step 2: Restart Windows Security Services

Windows Defender depends on several services. If these services are stopped, Defender won't work:

1. Press Windows + R to open Run dialog
2. Type services.msc and press Enter
3. Find these services in the list:
   • Windows Defender Antivirus Service
   • Windows Defender Advanced Threat Protection Service
   • Security Center
   • Windows Update
4. For each service, right-click and select "Properties"
5. Set "Startup type" to "Automatic"
6. If the service status shows "Stopped," click "Start"
7. Click "Apply" then "OK"
8. Restart your computer

Step 3: Check Group Policy Settings

Group Policy settings can disable Windows Defender, especially on computers managed by an organization or affected by malware:

Note: Group Policy Editor is only available in Windows Pro, Enterprise, and Education editions. If you have Windows Home, skip to Step 4.

1. Press Windows + R and type gpedit.msc
2. Navigate to: Computer Configuration > Administrative Templates > Windows Components > Microsoft Defender Antivirus
3. Double-click "Turn off Microsoft Defender Antivirus"
4. Select "Not Configured" or "Disabled"
5. Click "Apply" then "OK"
6. Also check: Computer Configuration > Administrative Templates > Windows Components > Microsoft Defender Antivirus > Real-time Protection
7. Set "Turn off real-time protection" to "Not Configured" or "Disabled"

Step 4: Run System File Checker

Corrupted system files can prevent Windows Defender from functioning. Windows includes a tool to repair these:

1. Right-click the Start button and select "Terminal (Admin)" or "Command Prompt (Admin)"
2. Type this command and press Enter: sfc /scannow
3. Wait for the scan to complete—this takes 10-30 minutes
4. If it finds and repairs issues, restart your computer
5. If SFC finds issues it can't repair, run this command next: DISM /Online /Cleanup-Image /RestoreHealth
6. After DISM completes, run sfc /scannow again
7. Restart and try enabling Windows Defender

Step 5: Check Registry Settings

Malware sometimes disables Windows Defender through registry modifications. Warning: Be careful editing the registry—incorrect changes can cause system problems.

1. Press Windows + R and type regedit
2. Navigate to: HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender
3. Look for a value named "DisableAntiSpyware"
4. If it exists and is set to 1, double-click it and change the value to 0
5. Click OK
6. Also check: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Defender\Real-Time Protection
7. Look for "DisableRealtimeMonitoring" - if it's set to 1, change it to 0
8. Close Registry Editor and restart your computer

Step 6: Update Windows

An outdated or buggy Windows version can cause Defender issues:

1. Go to Settings > Windows Update
2. Click "Check for updates"
3. Install all available updates, especially security updates
4. Restart when prompted
5. After updating, try enabling Windows Defender again

Step 7: Reset Windows Security App

If Windows Security app itself is corrupted, resetting it may help:

1. Go to Settings > Apps > Installed apps
2. Search for "Windows Security" in the list
3. Click the three dots next to it and select "Advanced options"
4. Scroll down and click "Repair" first - this attempts to fix issues without losing data
5. If repair doesn't work, click "Reset" to completely reinstall the app
6. Restart your computer

If Windows Defender Still Won't Turn On

For persistent issues, try these additional solutions:

• Run Windows Defender Offline - Some malware actively prevents Defender from running. In Windows Security, go to Virus & threat protection > Scan options > Microsoft Defender Offline scan. This will restart your PC and scan before Windows fully loads
• Check for malware manually - Download Malwarebytes from another device and scan your PC. Malware may be actively blocking Defender
• Create a new user account - Sometimes user profile corruption prevents Defender from working. Create a new admin account in Settings > Accounts > Family & other users
• Use System Restore - If Defender worked previously, restore to a point when it was functioning: type "Create a restore point" in Start, click "System Restore," and choose a restore point from before the problem started