Windows Defender may not be enabled due to third-party antivirus software conflicts, system settings problems, or corrupt system files. The solution is as follows: 1. Check and uninstall other antivirus software, restart it after restarting; 2. Run Windows Security Center troubleshooting to fix system problems; 3. Use administrator permissions to open a command prompt and execute sfc /scannow and DISM commands to repair system files; 4. Make sure that the Windows system has been updated to the latest version. The above steps usually solve most of the problems.

Sometimes Windows Defender doesn't turn on because of conflicts with other antivirus software, system settings, or corrupted system files. The good news is that most issues preventing it from running can be resolved without too much hassle.

Check if Another Antivirus Is Blocking It

Windows Defender automatically disables itself when it detects another antivirus program installed. If you recently installed third-party security software (like Norton, McAfee, or Bitdefender), that's likely the reason.

• Go to Settings > Update & Security > Windows Security > Virus & threat protection .
• Click “Manage settings” under Virus protection.
• If it says “Off (from another provider)” next to Real-time protection, then another antivirus is active.

To re-enable Windows Defender:

• Uninstall the third-party antivirus via Control Panel > Programs > Uninstall a program .
• Restart your computer and check again in Windows Security.

Run the Windows Security Center Troubleshooter

If no other antivirus is installed and Windows Defender still won't turn on, there might be a system issue. Windows has a built-in troubleshooter that can detect and fix common problems.

• Open Settings > Update & Security > Troubleshoot .
• Scroll down and click on Windows Security Center .
• Run the troubleshooter and follow any suggested fixes.

This tool often catches small glitches or permission issues that prevent Defender from starting properly.

Repair System Files Using Command Prompt

Corrupted system files can also stop Windows Defender from functioning correctly. Running a few commands in Command Prompt can help fix this.

• Right-click the Start menu and select Windows Terminal (Admin) or Command Prompt (Admin) .
• Type these commands one at a time, pressing Enter after each:

 sfc /scannow

 DISM /Online /Cleanup-Image /RestoreHealth

These commands scan for and repair corrupted system files. The process may take some time — don't interrupt it.

Once done, restart your PC and try turning on Windows Defender again.

Make Sure Windows Is Up to Date

Microsoft regularly releases updates that include bug fixes and security improvements. If your system isn't updated, you might be missing patches that affect Windows Defender.

• Go to Settings > Update & Security > Windows Update .
• Click Check for updates and install any available ones.
• Restart your computer after installing updates.

After updating, go back into Windows Security and see if Defender is now working.

That's usually all it takes to get Windows Defender running again. Most issues come down to conflicting software or minor system glitches — nothing too serious. Just start with the easiest fix first, like checking for other antivirus programs, and work your way through the steps if needed.

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