FIX: Windows Defender service won’t start on Windows 10

Madalina Dinita
by Madalina Dinita
Madalina has been a Windows fan ever since she got her hands on her first Windows XP computer. She is interested in all things technology, especially emerging technologies -- AI and DNA computing in... Read more
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  • If the Windows Defender cannot be started, you're left open to cyber-attacks and viruses.
  • Make sure to remove or disable any third-party antivirus solutions on the device.
  • Install the latest Windows and driver updates, and always keep them up-to-date.
  • You could also perform a System File Check scan and let the OS fix any detected issues.
fix windows defender not starting
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Windows Defender is one of the most popular antivirus programs worldwide, protecting millions of computers against vicious threads. However, many users report that their Windows Defender cannot be started.

Often, when users try to start Microsoft’s built-in antivirus, an error message appears on the screen informing them that the service couldn’t be started.

Many Windows 10 users reported that the Windows Defender service won’t start on their PC at all. Moreover, here are some other similar issues that users reported. and speaking of issues with Windows Defender.

  • Windows Defender service won’t start Windows 10, 8, 7 – According to users, this problem can appear on all versions of Windows, including both Windows 8 and 7. Even if you don’t use Windows 10, you should know that almost all of our solutions are compatible with older versions of Windows, so feel free to try them.
  • Windows Defender service won’t start error 577 – Sometimes error 577 can appear while trying to start Windows Defender service. To fix this problem, make sure that you don’t have any third-party antivirus installed on your system.
  • Windows Defender Security Center won’t open – Several users reported that Windows Defender Security Center won’t open at all. To fix this issue, check if you have the latest updates installed.
  • Windows Defender service won’t start access denied – This problem can appear due to issues with your permissions. To fix the problem, you need to adjust the security permissions of ProgramDataMicrosoft directory.
  • Windows Defender service keeps stopping – If Windows Defender service keeps stopping, the issue might be profile corruption. Simply create a new user profile and check if that solves the problem.

Windows Defender service won’t start, how to fix it?

1. Disable and remove third-party antivirus solutions

Running two antivirus solutions at the same time causes various technical issues. Use dedicated software removal tools to completely remove any third-party antivirus files.

If you don’t manage to fix the problem, you can always switch to a third-party antivirus solution. There are many great antivirus tools, and you should look for one that has lots of security features.

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2. Install the latest Windows Updates 

  1. Press Windows Key + I to open the Settings app.
  2. Now go to Update & Security section.
  3. Click Check for updates button.
    Windows Defender service won't start Windows 7

Windows will now check for available updates and download them in the background. Once the updates are downloaded, simply restart your PC to install them.

Sometimes you might be able to fix the Windows Defender service not starting simply by installing the latest updates. By keeping your system up to date, you’ll ensure that everything is running smoothly on your PC.

Windows 10 usually downloads the necessary updates automatically in the background, but due to certain bugs, you might skip an update or two.

3. Run an SFC scan

  1. Press Windows Key + X to open Win + X menu. Now select Command Prompt (Admin) or Powershell (Admin).
    Windows Defender service won't start Windows 8.1
  2. When Command Prompt opens, enter the following command and press Enter: sfc /scannow
    Windows Defender service keeps stopping
  3. SFC scan will now start. The scan can take up to 15 minutes, so don’t interrupt it.

According to users, sometimes Windows Defender service won’t start because of file corruption. Your system files can get corrupted and that can cause this error to appear.

Once the scan is finished, check if the problem still persists. If the issue is still present, or if you weren’t able to run SFC scan at all, you might want to try running DISM scan instead.

  1. Open Command Prompt as administrator.
  2. When Command Prompt opens, enter the following command: DISM /Online /Cleanup-Image /RestoreHealth
    Windows Defender service won't start error 577
  3. DISM scan will now start. The scan can take up to 20 minutes, sometimes more, so you need to be patient and not interrupt it.

Once the DISM scan is finished, check if the problem still persists. If the problem is still there or if you couldn’t run DISM scan before, be sure to repeat SFC scan and check if that solves the problem.

4. Clean your registry

Sometimes the Windows Defender cannot be started if there are issues with your registry. A corrupted registry entry can cause this issue to appear and you need to find and remove the problematic entry.

This is a complex task to perform manually, so it’s better to use special software for it. There are many great registry cleaners available that can help you with that problem.

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5. Check your environment variables

  1. Press Windows Key + S and enter advanced system settings. Select View advanced system settings from the menu.
    Windows Defender service won't start access denied
  2. Now click Environment Variables button.
    Windows Defender service keeps stopping
  3. Locate %ProgramData% variable and check if it’s set to C:ProgramData.
    • If not, change the variable accordingly.

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Environment variables are a useful feature that your system uses in order to access certain directories.

However, sometimes users or perhaps third-party applications can change your environment variables and cause this issue to appear.

This will make it so you cannot start the Windows Defender service but you can fix your environment variables manually by doing the following:

After making these changes, the problem should be resolved and Windows Defender should start working.

6. Change system permissions

  1. Go to the following directory: C:ProgramData
  2. Now locate the Microsoft directory and right-click it. Choose Properties from the menu.
    Windows Defender Security Center won't open
  3. Now go to the Security tab and click Advanced.
    Windows Defender service won't start access denied
  4. Now you should remove all inherited permissions. After doing that, save the changes and check if the problem is resolved.

According to users, sometimes your folder permissions can lead to this problem. If Windows Defender service won’t start on your PC, you might have to change your permissions.

This is an advanced procedure, and if you’re not familiar with permissions, you might want to skip this solution.

Keep in mind that this is a system folder, and any changes to this folder can cause issues to appear, so if you’re not familiar with system permissions, you might want to skip this solution.

7. Create a new user account

  1. Open the Settings app and go to the Accounts section.

    Windows Defender service won't start error 577
  2. Go to Family & other people on the menu on the left. In the right pane, click Add someone else to this PC.
    Windows Defender Security Center won't open
  3. Click I don’t have this person’s sign-in information.
    Windows Defender service won't start Windows 10
  4. Now select Add a user without a Microsoft account.
    Windows Defender service won't start error 577
  5. Enter the desired user name and click Next.
    Windows Defender Security Center won't open

If the Windows Defender service won’t start, you might be able to fix the problem simply by creating a new user account.

Sometimes your user account can get corrupted and that can cause this and other errors to appear. To fix the problems with a user account, follow the instructions above.

After creating a new user account, switch to it and check if the problem is still present. If not, you might have to switch to the newly created account and start using it instead of your old one.

8. Perform an in-place upgrade

  1. Download Media Creation Tool from Microsoft’s website and run it.
  2. Select Upgrade this PC now.
  3. Wait while setup prepares the necessary files.
  4. Select Download and install updates (recommended). Wait while the setup downloads the necessary files.
  5. Follow the instructions on the screen until you reach the Ready to install screen.
  6. Make sure that Keep personal files and apps appears on the recap list.
    • If not, click Change what to keep and select Keep personal files and apps from the list.
  7. Follow the instructions on the screen to complete the installation.

If the previous solutions didn’t fix the problem, you can try performing an in-place upgrade. By doing so, you’ll reinstall Windows 10, but you’ll keep all your files and applications.

Once the installation is finished, you’ll have a fresh installation of Windows and the problem should be resolved.

One last thing before we wrap up the article. If you’re looking for a new antivirus tool, take a look at this helpful list of the best antivirus tools with lifetime license and choose from there.

Not being able to start the Windows Defender service can be a problem, but we hope you managed to fix this issue with one of our solutions.

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