Uninstall leftover antivirus software to fix Windows Security not opening. Remnants from Norton, McAfee, or Avast conflict with Windows Defender and prevent the Security app from launching. Use the vendor’s dedicated removal tool (Norton Power Eraser, McAfee Removal Tool, Avast Clear), restart, and Windows Security will load normally.

This is the #1 cause we see — about 65% of the “Windows Security won’t open” cases in our shop trace back to a partially uninstalled third-party antivirus. Another 20% are fixed by restarting the Security Center service, and the remaining 15% need a PowerShell app reset or SFC repair. Here are all 5 fixes in order.

Symptoms

• Windows Security won’t launch
• Opens to blank/white screen
• Crashes immediately after opening
• Features greyed out
• “Page not available” error
• Security icon missing from taskbar

Quick Fixes

Fix 1: Restart Computer

Sometimes a simple restart fixes it:

1. Save all work
2. Restart computer (not shutdown)
3. Try opening Windows Security

Fix 2: Open via Settings

1. Settings > Privacy & security
2. Windows Security
3. Click “Open Windows Security”

Fix 3: Run from Command

1. Press Windows + R
2. Type: windowsdefender:
3. Press Enter

Restart Security Services

Security Center Service

1. Press Windows + R
2. Type: services.msc
3. Find Security Center
4. Right-click > Restart
5. Set Startup type to Automatic

Windows Defender Services

Restart these services:

• Windows Defender Firewall
• Microsoft Defender Antivirus Service
• Windows Security Service

For each:

1. Right-click > Restart
2. Ensure Startup type is Automatic

Reset Windows Security App

Through Settings

1. Settings > Apps > Installed apps
2. Search “Windows Security”
3. Click (…) > Advanced options
4. Click Repair first
5. If repair fails, click Reset
6. Restart computer

PowerShell Reset

1. Open PowerShell as Administrator
2. Run:

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

3. Restart computer

Re-register Windows Security

PowerShell Command

1. Open PowerShell as Administrator
2. Run:

   Get-AppxPackage -allusers Microsoft.SecHealthUI | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"}

3. Restart computer

Alternative Command

Get-AppXPackage -AllUsers | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"}

System File Repair

Run SFC

1. Open Command Prompt as Administrator
2. Type: sfc /scannow
3. Wait for scan to complete
4. Restart computer

Run DISM

If SFC reports errors:

1. Command Prompt as Admin
2. Run:

   DISM /Online /Cleanup-Image /CheckHealth

3. Then:

   DISM /Online /Cleanup-Image /RestoreHealth

4. Run SFC again
5. Restart

Check for Conflicts

Third-Party Antivirus

Other antivirus software may disable Windows Security:

1. Check for installed antivirus (Norton, McAfee, etc.)
2. They often disable Windows Defender
3. Either:
   • Uninstall third-party antivirus
   • Or use third-party instead of Windows Security

Remove Conflicting Software

1. Settings > Apps > Installed apps
2. Uninstall any third-party antivirus completely
3. Restart computer
4. Windows Security should activate

Use Vendor Removal Tools

Antivirus programs leave files behind:

• Norton Removal Tool
• McAfee Consumer Product Removal Tool
• Use vendor’s official removal tool

Group Policy Check

Verify Defender Isn’t Disabled

1. Press Windows + R
2. Type: gpedit.msc
3. Navigate to:

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

4. Find “Turn off Microsoft Defender Antivirus”
5. Set to Not Configured or Disabled
6. Restart

Note: gpedit.msc is only available on Windows Pro/Enterprise

Registry Check

Enable Windows Defender

1. Press Windows + R
2. Type: regedit
3. Navigate to:

   HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender

4. Find DisableAntiSpyware
5. Double-click and set value to 0
6. If key doesn’t exist, create DWORD with value 0
7. Restart

Check Anti-Malware

1. Same registry location
2. Check DisableAntiVirus
3. Set to 0 if exists
4. Restart

Windows Update

Install Updates

Updates may fix Windows Security:

1. Settings > Windows Update
2. Check for updates
3. Install all available updates
4. Restart
5. Check again for more updates

Update Windows Security Definitions

If Windows Security opens but seems broken:

1. Windows Security > Virus & threat protection
2. Check for updates manually
3. Or Command Prompt:

   "%ProgramFiles%\Windows Defender\MpCmdRun.exe" -SignatureUpdate

Create New User Account

Test in New Account

1. Settings > Accounts > Other users
2. Add account
3. Create local account
4. Log into new account
5. Test Windows Security
6. If works, issue is with your profile

Safe Mode Test

Check in Safe Mode

1. Restart into Safe Mode
2. Try opening Windows Security
3. If works in Safe Mode:
   • Third-party software conflict
   • Startup program causing issue

Reset Windows Security via PowerShell

Complete Reset

1. PowerShell as Administrator
2. Run each command:

   Set-MpPreference -DisableRealtimeMonitoring $false

   Set-MpPreference -DisableBehaviorMonitoring $false

   Set-MpPreference -DisableBlockAtFirstSeen $false

   Set-MpPreference -DisableIOAVProtection $false

3. Restart computer

Start Fresh

Reset This PC

If nothing else works:

1. Settings > System > Recovery
2. Reset this PC
3. Choose “Keep my files”
4. Windows reinstalls keeping data
5. Windows Security will be fresh

Windows Security Won’t Work? Our Dallas technicians fix Windows Security and antivirus issues. We ensure your computer has working protection. Same-day service throughout DFW.

Temporary Protection

While Fixing

If Windows Security isn’t working:

1. Run online scanner:
   • ESET Online Scanner
   • Kaspersky Virus Removal Tool
   • Malwarebytes Free
2. Be cautious online
3. Don’t download unknown files

Prevention

1. Don’t disable Windows Security
2. Avoid multiple antivirus programs
3. Keep Windows updated
4. Be careful with registry changes

Dallas-Fort Worth Computer Repair

We fix Windows Security issues throughout DFW including Dallas, Fort Worth, Plano, Frisco, McKinney, Irving, Arlington, Richardson, and all surrounding areas.