Basics

14 reasons why Windows security doesn’t work in Windows 10 (and how to fix it)

by Jonathan Dudamel
10 min read

A malfunctioning security center can leave your PC exposed — the most common cause is that Windows security doesn’t work in Windows 10 because a service, policy, or conflicting app is disabling it. This article explains the typical reasons this happens and walks you through practical fixes so Windows Security (Defender) is restored and keeping your PC safe.

You’ll learn the fastest fixes (restart services, remove conflicting AV), diagnostic steps (SFC/DISM, Safe Mode scans), policy and registry corrections, and preventive practices to avoid future failures.

Contents show

Key Takeaway

If Windows Security is not working, start by checking for a third-party antivirus and the Security Center and Windows Defender services; most problems are resolved by removing conflicts, enabling required services, updating Windows, or repairing system files with sfc /scannow and DISM.

Quick Fix Guide

Quick Fix Guide

Reason for the Problem Quick Solution
1. Third‑party antivirus installed Uninstall or disable the third‑party AV and reboot to allow Windows Security to re-enable.
2. Security Center service stopped Start the Security Center service and set startup to Automatic (Delayed Start).
3. Windows Defender service disabled Enable Microsoft Defender Antivirus Service (MsMpEng) or related Defender services.
4. Tamper Protection blocking changes Temporarily turn off Tamper Protection to apply fixes, then re-enable it.
5. Group Policy disables Defender Use gpedit.msc or registry to set Defender policies to Not Configured.
6. Outdated definitions/Windows build Run Windows Update and update Virus & threat protection definitions.
7. Malware interfering Run a Microsoft Defender Offline scan from Safe Mode or use rescue media.
8. Corrupted system files Run sfc /scannow and DISM /Online /Cleanup-Image /RestoreHealth.
9. RPC or service dependencies down Ensure Remote Procedure Call (RPC) and dependent services are running.
10. Incorrect date/time or certificates Fix Date & time settings and restart update services.
11. Network / proxy blocking updates Disable proxy, check firewall, and allow Defender update endpoints.
12. App corruption (Windows Security app) Use Settings > Apps > Windows Security > Advanced options > Repair/Reset.
13. Registry keys blocking Defender Remove disabling registry keys or restore from backup.
14. Corrupt user profile/system state Create a new admin account or use System Restore / Reset this PC.
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Detailed Fixes for “Windows security doesn’t work in Windows 10”

1. Third‑party antivirus installed and active

Why it causes the problem

  • Windows automatically disables real‑time protection when a third‑party antivirus is installed to prevent conflicts. If that AV is malfunctioning, your system may have no active protector.

Step-by-step solution

  1. Open Settings > Apps > Apps & features.
  2. Find your third‑party antivirus, select it, and click Uninstall.
  3. Reboot the PC.
  4. After reboot, open Windows Security (type “Windows Security” in Start). Confirm Virus & threat protection is active.
    Notes: If you want two layers, some AV products offer compatible modes, but generally run either Defender or the third‑party AV to avoid conflicts.

2. Security Center service stopped or disabled

Why it causes the problem

  • The Security Center service reports the status of antivirus, firewall, and updates. If stopped, the UI and notifications won’t reflect or manage protections.

Step-by-step solution

  1. Press Windows + R, type services.msc, press Enter.
  2. Find Security Center, double‑click it.
  3. Set Startup type to Automatic (Delayed Start).
  4. Click Start and then OK.
  5. Reopen Windows Security and check status.
    Tip: If the service won’t start, check Event Viewer for errors (Event Viewer > Windows Logs > System).

3. Windows Defender (Antivirus) service disabled

Why it causes the problem

  • The Defender engine (MsMpEng and related services) provide scanning and protection; if disabled, many features won’t work.

Step-by-step solution

  1. Open services.msc.
  2. Locate Microsoft Defender Antivirus Service (may appear as WinDefend).
  3. Set Startup type to Automatic and click Start.
  4. If the service is missing, Defender may be disabled via policy—see the Group Policy fix below.

4. Tamper Protection blocking fixes

Why it causes the problem

  • Tamper Protection prevents malicious or accidental changes to Defender settings, but it can block legitimate repairs.

Step-by-step solution

  1. Open Windows Security > Virus & threat protection.
  2. Under Virus & threat protection settings, click Manage settings.
  3. Turn Tamper Protection Off temporarily.
  4. Make required repairs (service start, updates), then turn Tamper Protection back On.
    Note: Only disable Tamper Protection temporarily; re-enable after fixes.

5. Group Policy blocking Defender

Why it causes the problem

  • Enterprise or previous AV installs can set Group Policy to disable Defender permanently.

Step-by-step solution (Windows 10 Pro/Education/Enterprise)

  1. Press Windows + R, type gpedit.msc, Enter.
  2. Navigate to Computer Configuration > Administrative Templates > Windows Components > Microsoft Defender Antivirus.
  3. Double‑click Turn off Microsoft Defender Antivirus, set to Not Configured or Disabled.
  4. Run gpupdate /force in an elevated Command Prompt.
    Registry alternative (Home edition)
  5. Press Windows + R, type regedit, Enter.
  6. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender.
  7. Remove DisableAntiSpyware or set its value to 0, then reboot.
    Warning: Editing Group Policy or registry requires care—export keys before changing.

6. Outdated definitions or Windows build

Why it causes the problem

  • Defender relies on up‑to‑date signatures and Windows updates to function properly and to fix bugs.

Step-by-step solution

  1. Open Settings > Update & Security > Windows Update and click Check for updates.
  2. Open Windows Security > Virus & threat protection > Protection updates and click Check for updates.
  3. Install updates and reboot.
    Tip: If updates fail, run Windows Update Troubleshooter (Settings > Update & Security > Troubleshoot).
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7. Malware interfering with Defender

Why it causes the problem

  • Sophisticated malware may disable Defender services or prevent updates.

Step-by-step solution

  1. Boot into Safe Mode with networking: Settings > Update & Security > Recovery > Advanced startup > Restart now > Troubleshoot > Advanced options > Startup Settings > Restart, then choose Safe Mode with Networking.
  2. In Safe Mode, open Windows Security and run Microsoft Defender Offline scan: Virus & threat protection > Scan options > Microsoft Defender Offline scan, then Scan now.
  3. If offline scan fails, create a bootable rescue USB from a reputable AV vendor and scan offline.
    Note: If you can’t run Defender, use another clean computer to create rescue media.

8. Corrupted system files (SFC/DISM)

Why it causes the problem

  • Damaged system files can break Defender components.

Step-by-step solution

  1. Open Command Prompt as Administrator (right‑click Start, choose Command Prompt (Admin) or Windows PowerShell (Admin)).
  2. Run: sfc /scannow
  3. After SFC completes, run:
    • DISM /Online /Cleanup-Image /CheckHealth
    • If issues: DISM /Online /Cleanup-Image /RestoreHealth
  4. Reboot and check Windows Security.
    Tip: DISM may take time and needs internet to repair from Windows Update.

9. RPC or service dependencies down

Why it causes the problem

  • Windows services depend on Remote Procedure Call (RPC) and other system services; if they’re down, Security services fail.

Step-by-step solution

  1. Open services.msc.
  2. Confirm Remote Procedure Call (RPC) and Windows Management Instrumentation (WMI) are Running and Startup type: Automatic.
  3. Restart any stopped dependencies, then restart Security Center and WinDefend.
    Note: Use Event Viewer to find dependency failure details.

10. Incorrect date/time or certificate issues

Why it causes the problem

  • Incorrect system time can break TLS/SSL and block update servers and signature validation.

Step-by-step solution

  1. Open Settings > Time & Language > Date & time.
  2. Turn Set time automatically on, or manually correct time zone and time.
  3. Reboot and try updates again.
    Tip: If on a domain, sync with domain controller time.

11. Network / proxy blocking updates

Why it causes the problem

  • Proxy settings, firewall policies, or DNS issues can prevent Defender from reaching Microsoft update servers.

Step-by-step solution

  1. Check basic connectivity: open a browser and visit https://www.microsoft.com.
  2. Disable proxy: Settings > Network & Internet > Proxy, set Use a proxy server off.
  3. Reset network: open elevated Command Prompt and run:
    • netsh winsock reset
    • netsh int ip reset
    • Reboot.
  4. Allow MsMpEng.exe and Windows Update through firewall if blocked.
    Tip: Corporate networks may need firewall exceptions; contact IT.

12. App corruption (Windows Security app)

Why it causes the problem

  • The Windows Security UI or app packages can be corrupted, preventing access or updates.

Step-by-step solution

  1. Open Settings > Apps > Apps & features.
  2. Find Windows Security, click Advanced options.
  3. Try Repair first; if not fixed, choose Reset.
  4. If Reset fails, open elevated PowerShell and run:
    • Get-AppxPackage Microsoft.SecHealthUI -AllUsers | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register “$($_.InstallLocation)\AppXManifest.xml”}
      Note: PowerShell reinstall commands should be used carefully; create a restore point first.
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13. Registry keys or policies left by old AV

Why it causes the problem

  • Leftover registry keys (from prior AV or admin scripts) can permanently disable Defender.

Step-by-step solution

  1. Open regedit (Windows + R, type regedit).
  2. Back up the registry: File > Export.
  3. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender.
  4. Delete keys like DisableAntiSpyware and DisableAntiVirus or set their values to 0.
  5. Reboot and check Defender.
    Warning: Only edit registry if comfortable; incorrect edits can harm the system.

14. Corrupt user profile or system state

Why it causes the problem

  • A damaged user profile or system configuration can block access to security settings.

Step-by-step solution

  1. Create a new local admin account: Settings > Accounts > Family & other users > Add someone else to this PC, then create user and change Account type to Administrator.
  2. Log in to the new account and check Windows Security.
  3. If still broken, use System Restore: Control Panel > Recovery > Open System Restore, choose a restore point before the issue.
  4. As a last resort, use Settings > Update & Security > Recovery > Reset this PC (choose keep files or remove everything).
    Note: Back up data before Reset.

Preventive maintenance and best practices

  • Keep Windows Update and Defender definitions up to date; enable automatic updates.
  • Use only one real‑time antivirus solution to avoid conflicts.
  • Enable Tamper Protection and Cloud‑delivered protection within Windows Security for better resilience.
  • Schedule periodic full scans and create a restore point before major changes.
  • Regularly run sfc /scannow and occasional DISM checks if you notice instability.
  • Maintain a good backup strategy (File History, OneDrive, or full-image backups) before doing system repairs.

FAQ

How can I run Windows Defender from PowerShell?

Open an elevated PowerShell and use: Start-MpScan -ScanType QuickScan (for quick) or Start-MpScan -ScanType FullScan (for full). To update definitions: Update-MpSignature.

Can I use third‑party antivirus together with Windows Security?

Windows allows some coexistence, but most third‑party AVs will disable Defender’s real‑time protection. Use one active real‑time AV; keep Defender as backup or periodic scanner if desired.

How do I check why Windows Security failed (logs)?

Open Event Viewer > Applications and Services Logs > Microsoft > Windows > Windows Defender and SecurityCenter logs to inspect error events and timestamps for troubleshooting.

Will reinstalling Windows fix Windows Security problems?

A clean reinstall will typically fix software corruption issues, but it’s a last resort. Try System Restore, Reset this PC (keep files), or repair steps before reinstalling.

How to prevent malware from disabling Defender in the future?

Enable Tamper Protection, keep automatic updates on, use strong browsing practices, avoid unknown downloads, and run periodic offline scans.

Conclusion

Most cases where Windows security doesn’t work in Windows 10 are caused by service conflicts, third‑party AV, policy settings, or corrupted system files; start with service checks, uninstall conflicting software, update Windows, and run SFC/DISM. Following the step‑by‑step fixes and preventive practices above will restore protection and help keep Windows Security working reliably.

About the author

Jonathan Dudamel

Jonathan Dudamel

I'm Jonathan Dudamel, an experienced IT specialist and network engineer passionate about all things Windows. I have deep expertise in Microsoft project management, virtualization (VMware ESXi and Hyper-V), and Microsoft’s hybrid platform. I'm also skilled with Microsoft O365, Azure ADDS, and Windows Server environments from 2003 through 2022.

My strengths include Microsoft network infrastructure, VMware platforms, CMMS, ERP systems, and server administration (2016/2022).

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