Antivirus & Security

Microsoft Defender Won't Turn On — Fix It

If Windows Security shows real-time protection as off and you can't switch it back on, here are the most common causes and the steps to fix them — no paid software needed.

Emily Carter Updated Jun 15, 2026 · 2 min read
Microsoft Defender Won't Turn On — Fix It
Photo: Dan Nelson · Unsplash
On this page
  1. Why Does This Happen?
  2. Fix 1: Check for Another Antivirus Programme
  3. Fix 2: Restart the Security Center Service
  4. Fix 3: Install Windows Updates
  5. Fix 4: Run the Windows Security Troubleshooter
  6. Fix 5: Repair Windows System Files

Seeing a message that real-time protection is off — and being unable to switch it back on — can feel alarming. In most cases it has a straightforward cause. Here's how to work through it.

Why Does This Happen?

The most common reasons Microsoft Defender turns off or becomes unresponsive are:

  • A third-party antivirus programme is installed (Defender disables itself to avoid conflicts)
  • A group policy setting is blocking it (common on work computers, less so at home)
  • Malware has deliberately disabled it
  • Windows needs an update
  • A Windows component needs repairing

Fix 1: Check for Another Antivirus Programme

Go to Settings > Apps > Installed apps and look for any third-party security software (such as AVG, Avast, McAfee, or Norton). If you find one you no longer use or didn't intentionally install, uninstall it. Windows Defender will usually re-enable itself within a few minutes of restart.

Fix 2: Restart the Security Center Service

  1. Press Windows + R, type services.msc, and press Enter.
  2. Scroll down to Security Center.
  3. Right-click it and choose Restart.
  4. Also check that Windows Defender Antivirus Service is set to Automatic and is running.

Fix 3: Install Windows Updates

Go to Settings > Windows Update > Check for updates. Install any pending updates and restart your computer. Updates often include fixes to Windows Security components.

Fix 4: Run the Windows Security Troubleshooter

  1. Press Windows + R, type ms-settings:troubleshoot, and press Enter.
  2. Click Other troubleshooters (or Additional troubleshooters on older versions).
  3. Find and run the Windows Security troubleshooter if available.

Fix 5: Repair Windows System Files

Open Command Prompt as administrator (search for cmd in the Start menu, right-click, Run as administrator), then type:

sfc /scannow

Press Enter and let it complete. This repairs corrupted system files that may be preventing Defender from running.

If malware has disabled Defender, a standard scan won't work. Try running a Microsoft Defender Offline scan by going to Scan options in Virus & threat protection and selecting the offline scan. If you still can't get Defender running, ask us — we can help.

Frequently asked questions

Defender says it's managed by my organisation but I'm on a home computer — why?

This sometimes happens after installing certain third-party software, or if a registry setting has been changed. Press <kbd>Windows</kbd> + <kbd>R</kbd>, type <code>regedit</code>, and navigate to <code>HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender</code>. If there is a value called <code>DisableAntiSpyware</code> set to 1, you can delete it. If you're not confident editing the registry, ask us for help first.

Can I use Windows without any antivirus while I fix this?

Keep that window as short as possible. Avoid downloading files or clicking unknown links until Defender is working again. Stick to websites you trust and don't open email attachments. If you need to be online, it's safer to do quick essential tasks only and then reconnect once protection is restored.

Emily Carter

Windows and home-networking specialist who has walked hundreds of readers through slow-PC, printer and Wi-Fi fixes.

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