Windows Defender Not Working? 3 Fixes to Try

Windows Defender is your built-in line of defense against malware on Windows 10 and 11. But sometimes it just doesn’t cooperate—maybe it won’t open, won’t turn on, or stops scanning altogether. If you’re stuck with a broken Defender, here are three fixes that actually work.

1. Check for Conflicting Antivirus Software

Windows Defender automatically disables itself if it detects another antivirus installed. Even a leftover registry entry from an old program can interfere.

What to do:

• Uninstall any third-party antivirus apps you’ve used.
• Restart your PC.
• Go to Settings > Privacy & Security > Windows Security > Virus & threat protection. If Defender is still off, move to the next fix.

2. Restart Windows Security Services

Sometimes Defender isn’t broken—it’s just not running. Restarting its services can bring it back to life.

Steps:

1. Press Win + R, type services.msc, and hit Enter.
2. Find these services:
   • Windows Defender Antivirus Service
   • Security Center
   • Windows Defender Firewall
3. Right-click each one and select Restart. If any are disabled, right-click > Properties and set Startup type to Automatic.

3. Run System File Checker (SFC)

Corrupted system files can stop Defender from working. SFC is a built-in tool that scans and fixes these files.

How to use it:

1. Open Command Prompt as Administrator.
2. Type this command and press Enter: sfc /scannow
3. Let it finish (it can take 10–15 minutes). Once done, restart your PC and try opening Defender again.

Still Not Working?

If Defender is still giving you trouble, it may be time to:

• Install updates via Settings > Windows Update
• Create a new user account to test if the issue is profile-related
• Or, as a last resort, perform a Windows repair install

Pro tip: Never leave your PC unprotected. If you can’t get Defender working quickly, install a free antivirus like Bitdefender or Avast as a temporary backup.

Got a different Defender issue or error message? Drop it in the comments, and I’ll help troubleshoot.