Windows Defender Not Working? 7 Fixes to Try

Microsoft’s Windows Defender ensures your PC is safe from various threats. If this tool stops working, your machine becomes vulnerable to many types of viruses and malware. Here’s how to resolve problems with Defender.

One common reason Defender stops working is that you’re using a third-party antivirus program. Other causes include corrupt system files, an obsolete Windows version, and more. We’ll walk you through the steps to get Defender working on your computer.

Note: Generally, using more than one full antivirus app isn’t a good idea (and most won’t work right if you try). However, you can use some antimalware apps (such as Malwarebytes) along with Windows Defender to shore up your defenses.

We assume you’ve already tried the basic solutions—like retrying a scan with Defender and restarting your PC—and are still having problems. The following methods should help you resolve your issue.

1. Update the Windows Operating System

A bug in your system can cause Windows Defender not to turn on or work as intended. One way to fix most Microsoft-acknowledged bugs is by updating your Windows system.

When you update, your system receives bug fixes, which help resolve various issues with your computer. Sometimes, you also get new features when you install a Windows update.

1. Launch Settings by pressing Windows + I.
2. Select Update & Security in Settings.
3. Choose Windows Update on the left.
4. Select Check for updates on the right.

5. Install the available updates.
6. Restart your PC.

2. Reset Windows Security

When Windows Defender doesn’t work or misbehaves, resetting the Windows Security app should be your first troubleshooting step. This helps because Defender is part of Windows Security and bringing the app back to factory values resolves many minor issues.

Resetting the app will clear the app’s saved data.

1. Open Start, search for Windows Security, select the down-arrow icon on the right, and choose App settings.
2. Scroll down the page and select Reset.

3. Choose Reset in the prompt.

4. Restart your PC by launching Start, selecting the Power icon, and choosing Restart.
5. Open Windows Security and enable or run Windows Defender.

3. Uninstall the Third-Party Antivirus Program

Windows Defender turns off when a third-party antivirus is running on your PC. You can try removing your installed antivirus tool to see if that fixes Defender’s issues.

Remove a Third-Party Antivirus Program

You remove an antivirus tool like how you do other Windows apps.

1. Open Settings by pressing Windows + I.
2. Select Apps in Settings.
3. Choose your antivirus on the list.
4. Select Uninstall.

5. Choose Uninstall in the prompt.
6. Reboot your PC.

When your PC turns on, launch Windows Security and see if Defender is working. If the issue persists, try cleaning up your antivirus’ leftover files to fix the problem.

Delete a Third-Party Antivirus’ Leftover Files

Microsoft has published a list of cleanup tools that you can use to remove an antivirus program from your PC completely. These tools dig deeper into your system’s directories, find the files associated with your antivirus, and delete those files.

Use the appropriate tool from the list on your PC and get rid of your antivirus tool’s leftover files. When you’re done, reboot your PC.

4. Restart the Security Center Service

Windows uses various services to keep your PC’s functions running. One of these is a Security Center service, which is related to the Windows Defender tool. You can try turning off and turning on this service to resolve your problem.

1. Open Run by pressing Windows + R.
2. Type the following and press Enter: services.msc
3. Find Security Center in the service list on the right.

4. Right-click Security Center and choose Restart.

5. Turn On Windows Defender From Registry or Group Policy Editor

If you have trouble enabling Windows Defender from the Windows Security app, try the alternative methods like Windows Registry and Local Group Policy Editor to activate the tool.

Use the Windows Registry method if you’re running the Windows Home edition. If you’re on the Pro or Enterprise edition, use the Local Group Policy Editor method.

Activate Windows Defender From Windows Registry

1. Press Windows + R to open Run, type the following in the Run box, and press Enter: regedit
2. Select Yes in the User Account Control prompt.
3. Head to the following path in Registry Editor:
   HKEY_LOCAL_MACHINESOFTWAREPoliciesMicrosoftWindows Defender
4. Access the DisableAntiSpyware entry on the right. If you don’t see this entry, create it by right-clicking anywhere blank and choosing New > DWORD (32-bit) Value.

5. Enter 0 in the Value data field and select OK.

6. Close Registry Editor.

Windows Defender is now enabled on your PC.

Turn On Windows Defender From Local Group Policy Editor

1. Open Run by pressing Windows + R, type the following in Run, and press Enter: gpedit.msc
2. Navigate to the following path in Local Group Policy Editor:
   Computer Configuration > Administrative Templates > Windows Components > Microsoft Defender Antivirus
3. Open the Turn off Microsoft Defender Antivirus entry on the right.

4. Select Disabled and choose Apply followed by OK at the bottom.

5. Close Local Group Policy Editor.

Windows Defender is now activated.

6. Perform a Clean Boot on Your Windows PC

One possible reason Windows Defender isn’t working is that your other installed apps are causing interference with the tool. You can verify that by clean booting your system, which only loads the essential system files to turn on your PC.

If you can enable and use Defender when you’ve clean booted your PC, one or more of your installed apps are the culprit. In this case, manually verify your app list and remove the apps that you believe are suspicious.

7. Fix Windows’ Corrupt System Files

When Windows system files become corrupt, you experience unexpected issues on your machine, including Defender not working. Luckily, Windows includes a tool that you can use to find and fix all the faulty system files on your computer.

1. Right-click Start and choose Command Prompt (Admin).
2. Select Yes in the User Account Control prompt.
3. Type the following in Command Prompt and press Enter: DISM.exe /Online /Cleanup-image /Restorehealth
   

4. Wait for the command to finish executing.
5. Next, run the following command: sfc /scannow
   

6. Wait for the command to find and fix problematic files.

Fix the Broken Windows Defender Tool on Your Computer

It’s essential to keep Windows Defender running as the tool ensures the safety of your data. However, sometimes, the tool experiences hiccups and doesn’t work as expected. In such a situation, you can follow the above methods to eliminate the error.

Once you’ve fixed the issue, you can run a full scan to ensure no threats are sitting on your computer.