How to Fix Windows Security Not Opening in Windows 11 and 10

Common causes

A third-party antivirus is installed and registered with Windows, so Microsoft Defender Antivirus switches itself off as designed.
An expired antivirus trial, often preinstalled on new laptops, or leftovers from an incomplete uninstall still tell Windows another product is protecting the PC.
The Windows Security app package is damaged, causing a blank window, an instant crash, or a 'You'll need a new app to open this windowsdefender link' message.
The Security Center or Microsoft Defender Antivirus services have stopped or have been set to the wrong startup type.
Damaged Windows system files or component store problems, often after an interrupted or failed update.
Group Policy or registry settings that turn off Defender or hide parts of Windows Security, sometimes left by tweak tools or an old work setup.
Malware that deliberately disables Defender, blocks the Windows Security app, or adds exclusions so it can't be detected.
Pending Windows or security intelligence updates that haven't finished installing because the PC hasn't restarted.

Step-by-step fixes

Step 1

Restart and install pending updates

Start simple. Select Start > Power > Restart rather than Shut down, because Fast Startup means a shutdown doesn't fully reset Windows. Then open Settings > Windows Update in Windows 11 (Settings > Update & Security > Windows Update in Windows 10), select Check for updates, and install everything offered, including security intelligence updates for Microsoft Defender Antivirus. If Restart now appears, restart again. Updates often replace the Windows Security app and Defender platform files, which can clear a broken or blank window on their own. After restarting, open Windows Security from the Start menu, or press Windows key + R, type windowsdefender: and press Enter. Success is the Security at a glance page appearing, with green checkmarks or clear actions to take.

Step 2

Check whether another antivirus has turned Defender off

Microsoft Defender Antivirus switches off automatically when another antivirus registers with Windows, which is expected rather than a fault. Open Control Panel > System and Security > Security and Maintenance, expand Security, and look at Virus protection to see which product Windows thinks is active. If it lists an antivirus you no longer use, such as an expired McAfee or Norton trial, uninstall it from Settings > Apps > Installed apps (Windows 10: Settings > Apps > Apps & features). Then run the vendor's official removal tool, such as McAfee's Consumer Product Removal tool or Norton's remover tool, to clear leftovers, and restart. Defender should turn itself back on shortly afterward. Success is Virus & threat protection showing Microsoft Defender Antivirus active with real-time protection on.

Step 3

Reset or re-register the Windows Security app

If the app opens to a blank screen, closes instantly, or shows a 'You'll need a new app' message, reset it. In Windows 11, open Start, type Windows Security, right-click the result, select App settings, and then select Reset. If that option is missing or doesn't help, or you're on Windows 10, right-click Start and choose Terminal (Admin) or Windows PowerShell (Admin), then run: Get-AppxPackage Microsoft.SecHealthUI -AllUsers | Reset-AppxPackage. Wait for the command to finish without errors, then restart the PC. Resetting rebuilds the app's interface; it doesn't uninstall Microsoft Defender Antivirus or remove its protection. If PowerShell reports that the command isn't recognized, install the latest Windows updates first. Success is Windows Security opening normally instead of a blank window or error.

Step 4

Make sure the security services are running

Press Windows key + R, type services.msc, and press Enter. Find Security Center: it should be Running with a startup type of Automatic (Delayed Start). If it's stopped, double-click it, set that startup type, select Start, and then OK. Next, find Microsoft Defender Antivirus Service, which should be Running when Defender is your only antivirus. Windows protects the Defender services, so their startup options are usually greyed out, which is normal. For a quick status check, open an administrator PowerShell window and run Get-MpComputerStatus; AMServiceEnabled, AntivirusEnabled, and RealTimeProtectionEnabled should all show True. If Security Center won't start or keeps stopping, continue to the system file repair. Success is both services running after a restart.

Step 5

Repair Windows system files with DISM and SFC

Damaged system files can stop Windows Security or Defender from loading. Right-click Start and open Terminal (Admin) or Windows PowerShell (Admin), then run DISM /Online /Cleanup-Image /RestoreHealth. This repairs the Windows component store using Windows Update and can take a while, sometimes appearing stuck at a percentage, so let it finish. Next, run sfc /scannow, which checks protected system files against the repaired store and replaces damaged ones. When SFC reports that it found corrupt files and successfully repaired them, or that it did not find any integrity violations, restart the PC and try Windows Security again. If SFC says some files couldn't be repaired, restart and run both commands once more. Success is a clean SFC result and a working Windows Security app.

Step 6

Scan for malware that disables Defender

Some malware turns off Defender, adds exclusions, or blocks Windows Security from opening, so check with a tool that doesn't depend on Defender. Download Microsoft Safety Scanner or ESET Online Scanner from the official site, or use Malwarebytes, and run a full scan. If Defender still works in the background, you can also start an offline scan from an administrator PowerShell window by running Start-MpWDOScan; save your work first, because the PC restarts. After cleaning, open Windows Security > Virus & threat protection > Manage settings, review Exclusions for folders, files, or processes you didn't add, and make sure Tamper Protection is on so malware can't quietly change these settings again. Success is a clean scan and no unexplained exclusions.

Step 7

Remove Group Policy or registry settings that disable Defender

Warning: back up the registry first (Registry Editor > File > Export), and skip this on a work or school PC, where IT may manage Defender deliberately. If Windows Security says your IT administrator has limited access, or a setting is managed by your administrator, a policy is involved. On Windows Pro, run gpedit.msc, go to Computer Configuration > Administrative Templates > Windows Components > Microsoft Defender Antivirus, set Turn off Microsoft Defender Antivirus to Not configured, and check the Real-time Protection folder too. On any edition, open regedit and go to HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender. Delete values such as DisableAntiSpyware, and DisableRealtimeMonitoring in the Real-Time Protection subkey. Also check the Windows Defender Security Center key beside it for settings that hide app pages. Restart. Success is the administrator message disappearing.

Step 8

Repair Windows with an in-place reinstall

If nothing else works, reinstall Windows over itself while keeping your files and apps. Back up important files first as a precaution. In Windows 11, go to Settings > System > Recovery and, under Fix problems using Windows Update, select Reinstall now. This downloads and reinstalls your current version of Windows and can take an hour or more. If that option isn't available, or you're on Windows 10, download the Installation Assistant or Media Creation Tool from Microsoft's website, run the upgrade, and choose to keep personal files and apps. An in-place repair replaces system files, including the Windows Security app and Defender components, without wiping your data. Success is Windows Security opening normally, with Defender active, after the repair finishes.

How to prevent it

Run only one real-time antivirus at a time, and use the vendor's official removal tool when you uninstall a suite or trial.
Keep Tamper Protection on in Windows Security > Virus & threat protection > Manage settings.
Avoid debloat and privacy tweak scripts that disable Defender, Windows Update, or security services.
Install Windows updates regularly and restart when prompted so app and platform updates can finish.
Check Windows Security after installing or removing any security software to confirm something is protecting the PC.

Tools that can help

Windows Security can almost always be repaired with the free steps above. If malware keeps switching Defender off, a standalone scanner helps you confirm the PC is clean, and a paid suite is a reasonable choice if you'd rather not depend on Defender.

Best for cleanup

Malwarebytes

The free Malwarebytes scanner is a strong second opinion for malware, adware, and unwanted programs, while Premium adds real-time, ransomware, and web protection that can run alongside Microsoft Defender.

Visit Malwarebytes

Top pick

Bitdefender

Bitdefender combines top-tier malware and ransomware protection with web filtering across browsers and a secure banking browser, with extras such as unlimited VPN and identity monitoring on higher tiers.

Visit Bitdefender

Best free one-time scan

ESET Online Scanner

ESET's free one-time scanner downloads its current detection engine, scans and cleans the PC, and works without relying on Microsoft Defender or conflicting with your existing antivirus.

Get ESET Online Scanner

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What to do next if this fails

Move to the next fix instead of repeating the same step multiple times.
Check the related guides in this cluster before attempting a full reset.
If startup, update, and corruption symptoms overlap, widen the diagnosis instead of treating one error in isolation.

FAQ

What does 'You'll need a new app to open this windowsdefender link' mean?

It means Windows can't find a working Windows Security app to handle the request, usually because the app package is damaged or was removed, sometimes by a 'debloat' script. Resetting the app with the PowerShell command in this guide usually fixes it. If the package is missing entirely, run DISM and SFC, and if that doesn't help, do an in-place repair so Windows reinstalls its built-in apps.

Is it a problem that Defender is off when I have another antivirus?

No, that's by design. Windows allows only one active real-time antivirus to avoid conflicts, so Microsoft Defender Antivirus steps aside when another product registers. Windows Security will list that product under Virus & threat protection. It only becomes a problem if the other product has expired, was uninstalled badly, or has stopped updating, in which case remove it fully so Defender can turn back on.

Can I run Microsoft Defender alongside another antivirus?

Not with both providing real-time protection. However, when another antivirus is active, Windows Security offers Periodic scanning under Virus & threat protection > Microsoft Defender Antivirus options. It lets Defender run occasional scans as a second opinion without interfering with your main product. Turn it on if you want an extra check, but leave real-time protection to the antivirus you've chosen.

Why does Windows Security say my IT administrator has limited access?

That message appears when a Group Policy or registry policy controls Defender or hides parts of the app. On a work or school PC it's intentional, so talk to your IT team. On a personal PC, it's usually left over from a privacy or tweak tool, an old workplace setup, or malware. Scan for malware first, then remove the policies using the Group Policy and registry step in this guide.

Why can't I turn real-time protection back on?

The toggle may be greyed out or keep switching off because another antivirus is registered, a policy is disabling Defender, or malware is interfering. Check Control Panel > Security and Maintenance to see which antivirus Windows thinks is active, look for 'managed by your administrator' messages, and run a standalone scan. Note that switching real-time protection off by hand is temporary; Windows turns it back on automatically.

How can I tell whether Defender is actually protecting my PC?

Open Windows Security > Virus & threat protection: it should show Microsoft Defender Antivirus with no actions needed. For a precise check, run Get-MpComputerStatus in PowerShell and confirm AntivirusEnabled and RealTimeProtectionEnabled are True and the signature dates are recent. You can also use the harmless EICAR test file, which our guide to checking whether your antivirus works explains step by step.