Unable to turn on Windows Defender on Windows 10

If you can’t turn on Windows Defender on Windows 10, one of the fixes below should help. Start with the first one and work your way down the list.

Update (October 2026): Microsoft ended support for Windows 10 on October 14, 2025. On newer versions of Windows 10 and on Windows 11, Windows Defender is called Microsoft Defender Antivirus, and you manage it in the Windows Security app. Most of these checks also apply to Windows 11.

If you turned Defender off yourself with my guide on how to disable Windows Defender completely, fixes 5 and 6 below undo those changes.

In this article

1. Can’t Turn On Windows Defender in Windows 10: Quick Checklist
2. 1. Check If You Have Another Security Program Installed
3. 2. Check the Date and Time on Your PC
4. 3. Run Windows Update
5. 4. Check Internet Zone and Proxy Settings
6. 5. Check the Group Policy Setting
7. 6. Check the Registry Setting
8. 7. Check the Status of the Defender Service
9. 8. Scan Your PC with a Portable Antivirus
10. 9. Check the Value of AllowUserUIAccess

Can’t Turn On Windows Defender in Windows 10: Quick Checklist

1. Check if you have another security program installed
2. Check the date and time on your PC
3. Run Windows Update
4. Check the Internet zone and proxy settings
5. Check the Group Policy setting
6. Check the registry setting
7. Check the status of the Defender service
8. Scan your PC with a portable antivirus
9. Check the value of AllowUserUIAccess

1. Check If You Have Another Security Program Installed

Windows Defender turns itself off when it detects a third-party antivirus. Windows is designed to detect installed security software, and you often see a notification about it in the Action Center. Having several security programs at the same time is a common problem: they conflict with each other and cause more trouble than protection. Frequent freezes and app crashes are typical signs.

To avoid this, Windows Defender switches off when another security program is installed. If that program also has a firewall, Windows Firewall stops working too. So if you want Windows Defender to work, uninstall the third-party security software and restart your PC.

Many people don’t even know they have another antivirus. New laptops often come with a trial version of Norton, McAfee or a similar program. Installers of programs like Flash or Java also offered to install a free security scanner, and most people did not notice. If you are not sure, check your installed apps in Settings > Apps.

After you remove the other program, you may need to turn Defender back on manually:

• Current Windows 10 versions: open Windows Security > Virus & threat protection > Manage settings and turn on Real-time protection.
• Older Windows 10 versions: type Windows Defender in the search box and press Enter. Click Settings and make sure Turn on real-time protection (recommended) is checked.

2. Check the Date and Time on Your PC

A wrong date or time on your PC can also stop Windows Defender from working properly. It sounds strange, but many Windows functions depend on the system date and time, so a wrong clock can cause unusual behavior.

Go to Settings > Time & Language > Date & time and make sure the date, time and time zone are correct (turning on Set time automatically is the easiest way). Then try to turn Windows Defender on again.

3. Run Windows Update

If Windows is not up to date, Windows Defender and other core Windows apps can have problems. Security software always needs the latest definition updates and Windows updates to keep your PC safe.

1. Run Windows Update and install everything it offers.
2. Then update Defender itself: open Windows Security > Virus & threat protection > Protection updates and click Check for updates.
3. Check if Windows Defender works now.

4. Check Internet Zone and Proxy Settings

The fixes above solve the most common cases, but smaller issues can also affect Windows Defender. One of them is a wrong zone setting in Internet Explorer. You can fix it by resetting Internet Explorer to its default settings (Control Panel > Internet Options > Advanced > Reset).

Also, if you use a proxy server, Windows Defender cannot download updates. In that case, set your proxy for Windows services too:

1. Press Windows + X and select Command Prompt (Admin) or Windows PowerShell (Admin).
2. Type one of the following commands and press Enter. Replace the example address and port with your own proxy server.

NETSH WINHTTP SET PROXY 1.1.1.1:8080

or, if your proxy server has a name:

NETSH WINHTTP SET PROXY MYPROXY.NET:8080

Restart your PC and check if Defender works.

5. Check the Group Policy Setting

Press Windows + R, type gpedit.msc and press Enter to open the Group Policy Editor. Then go to:

Computer Configuration > Administrative Templates > Windows Components > Windows Defender Antivirus

On newer versions of Windows, the last folder is called Microsoft Defender Antivirus.

1. In the right pane, double-click Turn off Windows Defender Antivirus (or Turn off Microsoft Defender Antivirus).
2. Select Not Configured.
3. Click Apply, then OK.

Note: The Group Policy Editor is only included in Windows 10 Pro, Enterprise and Education. On Windows 10 Home, use the registry fix below. If Windows Security says Some settings are managed by your organization, you can also reset all Group Policy settings to default.

6. Check the Registry Setting

Press Windows + R, type regedit and press Enter to open the Registry Editor. Then go to this key:

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender

1. Find the DisableAntiSpyware value. If it is not there, create a new DWORD (32-bit) Value with this name.
2. Double-click it and set its Value data to 0.
3. Click OK and close the Registry Editor.

7. Check the Status of the Defender Service

Press Windows + R, type services.msc and press Enter to open Services. Make sure the Windows Defender service (called Microsoft Defender Antivirus Service on newer versions) is running and its Startup type is set to Automatic.

8. Scan Your PC with a Portable Antivirus

Malware itself can also be the reason why Windows Defender does not work properly. Download the Windows Defender Offline tool or another standalone antivirus scanner and run a full scan.

On current versions of Windows 10, Microsoft Defender Offline is built in: open Windows Security > Virus & threat protection > Scan options, select Microsoft Defender Offline scan and click Scan now. Your PC restarts and runs the scan before Windows loads.

9. Check the Value of AllowUserUIAccess

If the Virus & threat protection option has disappeared from Windows Security, try this:

1. Run the Registry Editor as administrator.
2. Go to this key:

   Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender\Policy Manager

3. Set the value of AllowUserUIAccess to 1.

These are the most common reasons why Windows Defender does not start. Restart your PC after each change and try to turn Defender on again.

Source: this guide is based on an article by TheWindowsClub, which also has more tips for when Windows Defender is turned off or not working.

Source: TheWindowsClub