Windows Defender (now called Windows Security) may fail to work due to a combination of system conflicts, corrupted files, or misconfigured settings. The issue manifests in various ways—freezing on launch, failing to open, or displaying error messages—across Windows 10 and 11. Common root causes include interference from third-party antivirus software, disabled core services, outdated system files, or incorrect registry/group policy configurations. Users report success with troubleshooting steps like resetting the app, running system repairs, or adjusting service settings, though some cases require deeper interventions like clean boots or repair installs.

Key findings from the sources:

• Third-party antivirus conflicts are the most frequently cited cause, with solutions recommending temporary disabling or complete removal ^[5][6][7]
• System file corruption is addressable via sfc /scannow and DISM commands, with multiple sources confirming their effectiveness ^[4][7][10]
• Service and registry issues often require manual checks, such as verifying the Security Center service status or modifying registry keys ^[2][3][9]
• App-specific resets (via Settings or PowerShell) resolve freezing/crashing in many cases, though some users report persistent issues requiring repair installs ^[1][8]

Core Solutions for Windows Defender Malfunctions

System-Level Repairs and Service Checks

Windows Defender relies on several background services and system integrity components. When these are disrupted, the app may fail to launch or function properly. The most consistently recommended fixes involve repairing system files and ensuring critical services are operational.

System File Checker (SFC) and Deployment Imaging Service and Management Tool (DISM) are the primary tools for addressing corruption. The sfc /scannow command scans for and repairs corrupted Windows files, while DISM focuses on the system image. Multiple sources emphasize running these in sequence:

• Open Command Prompt as Administrator and execute:
• sfc /scannow (wait for completion, then restart)
• DISM /Online /Cleanup-Image /RestoreHealth ^[4][7][10]
• Users report these commands resolve issues in ~60-70% of cases where Defender fails due to file corruption ^[4].

Service-related fixes target the Security Center and Windows Defender services, which must be running for the app to function:

• Press Win + R, type services.msc, and verify these services are set to Automatic and running:
• Security Center
• Windows Defender Antivirus Service
• Windows Defender Firewall ^[3][9]
• If missing, recreate the Security Center service via PowerShell:

New-Service -Name "SecurityCenter" -BinaryPathName "C:\Windows\System32\svchost.exe -k LocalServiceNetworkRestricted" -DisplayName "Security Center" -StartupType Automatic

For persistent service failures, a clean boot isolates conflicts by disabling non-Microsoft startup items:

1. Open msconfig (via Win + R).
2. Under Services, check Hide all Microsoft services, then disable all remaining.
3. Restart and test Defender. If functional, re-enable services one by one to identify the culprit ^[5].

App-Specific and Configuration Fixes

When Defender’s app interface malfunctions (e.g., freezing or crashing), resetting or reinstalling the component often resolves the issue. The Windows Security app (Defender’s modern UI) can be reset without affecting core antivirus protections:

1. Reset via Settings: - Navigate to *Settings > Apps > Installed apps. - Locate Windows Security, click the three dots, select Advanced options, then Reset* ^[1][4].
2. PowerShell Reinstallation (for severe corruption): - Run as Administrator:

Get-AppxPackage Microsoft.SecHealthUI -AllUsers | Reset-AppxPackage

or reinstall with:

Add-AppxPackage -Register -DisableDevelopmentMode "C:\Windows\SystemApps\Microsoft.Windows.SecHealthUI_cw5n1h2txyewy\AppxManifest.xml"

• Registry Editor (regedit):
• Navigate to HKEYLOCALMACHINE\SOFTWARE\Policies\Microsoft\Windows Defender.
• Ensure DisableAntiSpyware is set to 0 (or delete the key if present) ^[2][9].
• Group Policy (gpedit.msc):
• Navigate to *Computer Configuration > Administrative Templates > Windows Components > Microsoft Defender Antivirus.
• Verify Turn off Microsoft Defender Antivirus* is set to Not Configured or Disabled ^[6][9].

• Temporarily disabling the third-party AV to test Defender functionality ^[5][6].
• Completely uninstalling conflicting software via *Settings > Apps* or the vendor’s removal tool (e.g., Norton Remove and Reinstall Tool) ^[7].
• Ensuring real-time protection is enabled in Defender after removal:
• Open *Windows Security > Virus & threat protection > Manage settings and toggle Real-time protection* to On ^[6].

For users on Windows 11 IoT LTSC or specialized editions, Defender may be intentionally restricted. In such cases, enabling it requires:

• Editing the registry to force-enable features (risky; backup first) ^[2].
• Contacting Microsoft Support for enterprise-specific configurations.