Troubleshooting Guide: “Windows Security Can’t Be Started” — Solutions and Fixes

If you see the error “Windows Security can’t be started” on your Windows PC, it usually means that the built‑in Windows protective services (including Microsoft Defender Antivirus) are failing to initialize. This can happen due to corrupted system files, misconfigured services, conflicting security software, or recent updates gone wrong. Fortunately, there are several reliable solutions you can try to get Windows Security working again.

This step‑by‑step troubleshooting guide covers all major fixes for Windows 10 and Windows 11, explaining each solution clearly and safely — so you can restore full protection on your device.

Why This Error Happens

Before diving into fixes, it helps to understand common root causes:

• Disabled services required by Windows Security
• Corrupted system files or update issues
• Interference from third‑party antivirus software
• Group Policy or registry misconfigurations
• Software conflicts or malware interference

We’ll walk through fixes from simplest to most advanced.

Getting Started: Before You Fix Anything

1. Restart Your PC

A reboot clears temporary glitches and resets services that may have failed to start.

2. Check Windows Updates

Make sure your system is up to date:

1. Settings → Windows Update
2. Click Check for updates
3. Install all available patches

In many cases, missing updates can break security services.

Fix 1: Ensure Required Services Are Running

Windows Security relies on several system services. If these are stopped or disabled, the security app won’t start.

1. Press Windows + R, type services.msc, and press Enter
2. Look for the following services:
   • Security Center
   • Windows Defender Antivirus Service
   • Windows Defender Firewall
   • Windows Defender Security Center Service (on some systems)
3. For each one:
   • Right‑click → Properties
   • Set Startup type to Automatic
   • Click Start (if stopped)

If these services fail to start, restart your PC and check again.

Fix 2: Scan and Repair Corrupted System Files

Corrupted system files often cause Windows Security errors. Use the built‑in repair tools:

System File Checker (SFC)

1. Open Command Prompt as Administrator
2. Run: sfc /scannow

This checks integrity and attempts to repair corrupted system files.

DISM (if SFC Finds Issues)

1. Still in elevated Command Prompt: DISM /Online /Cleanup-Image /RestoreHealth

After DISM completes, run sfc /scannow again.

Fix 3: Disable Conflicting Third‑Party Antivirus Software

If you installed another antivirus program, it may disable Windows Security to avoid conflicts. Common examples include Norton, McAfee, Avast, and Bitdefender.

How to Disable It

1. Open the third‑party antivirus interface
2. Locate Real‑time protection or Shield Controls
3. Turn them off temporarily

Alternatively, use the vendor’s uninstall tool to remove the software completely, then restart your PC. After removal, Windows Security should re‑enable itself automatically.

Fix 4: Reset the Windows Security App

Sometimes the app itself becomes corrupted. Resetting it often fixes start‑up errors:

1. Settings → Apps → Apps & features
2. Scroll to Windows Security
3. Click Advanced options
4. Choose Reset

This resets the app without harming your files.

Fix 5: Check Group Policy Settings (Windows Pro / Enterprise)

If Group Policy disables security features, Windows Security won’t start.

1. Press Windows + R, type gpedit.msc, and press Enter
2. Navigate to: Computer Configuration → Administrative Templates → Windows Components → Microsoft Defender Antivirus
3. Ensure Turn off Microsoft Defender Antivirus is set to Not Configured or Disabled.

After adjusting, restart your PC.

Fix 6: Fix Windows Defender in the Registry (Advanced)

Warning: Editing the registry incorrectly can harm your system. Back up the registry first.

1. Press Windows + R, type regedit, and press Enter
2. Navigate to: HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender
3. If you see a DWORD named DisableAntiSpyware, right‑click it and Delete it.

After this, restart your PC. Windows should automatically re‑enable Defender.

Fix 7: Re‑Register Windows Security DLLs

If core libraries fail to load, re‑registering them can help.

1. Open Command Prompt as Administrator
2. Run these commands one by one:

regsvr32 /s atl.dll
regsvr32 /s wuapi.dll
regsvr32 /s wuaueng.dll
regsvr32 /s wups.dll
regsvr32 /s wups2.dll

Restart your PC afterward.

Fix 8: Create a New Admin User Account

If user profile corruption prevents Windows Security from starting, a fresh admin account might help.

1. Settings → Accounts → Family & other users
2. Click Add account
3. Choose I don’t have this person’s sign‑in information
4. Select Add a user without a Microsoft account
5. Create credentials and mark the account as Administrator
6. Log in to the new account and check Windows Security

If this works, the issue may be limited to your old profile.

Fix 9: System Restore to a Previous Point

If Windows Security worked recently, restoring your system to a previous point can fix recent errors.

1. Control Panel → Recovery → Open System Restore
2. Choose a restore point before the error began
3. Follow prompts to restore

This won’t affect your personal files but will revert system changes.

Fix 10: Repair or Reinstall Windows (Last Resort)

If none of the above works, you may need to repair install Windows:

In‑Place Upgrade

1. Download the Windows 10/11 Installation Media from Microsoft
2. Run Setup.exe
3. Choose Keep personal files and apps

This refreshes core system files without losing data.

Preventing the Error in the Future

Here are proactive steps to avoid Windows Security failures:

• Keep Windows updated regularly
• Avoid running outdated or multiple antivirus tools simultaneously
• Don’t disable security services manually
• Use trusted apps from Microsoft Store or reputable developers

FAQs: Quick Answers

Q: Can a virus cause Windows Security to fail?
Yes — malware can disable security services. Running an offline scan (Windows Defender Offline) can help detect persistent threats.

Q: Will uninstalling another antivirus fix the error?
Often yes, because third‑party AV can disable Defender and cause start‑up failures.

Q: Does Windows Security reset remove my settings?
The reset may revert configurations, but won’t delete personal files.

Q: Is this issue common after updates?
Yes — update interruptions or corrupted patches can break security services.

Conclusion

The “Windows Security can’t be started” error can be alarming, but it’s usually fixable using systematic troubleshooting. Starting with basic checks and progressing to advanced fixes — such as service verification, system file repair, policy adjustments, or reinstalling Windows — you can restore full security functionality.

Always keep your system updated and avoid disabling protective features unless absolutely necessary. With the steps in this guide, you’ll regain Windows Security and help safeguard your PC.