Windows Defender is one of the most popular antivirus programs worldwide, protecting millions of computers against vicious threads. However, sometimes starting Windows Defender proves to be a very difficult, as many users report.
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.
Windows Defender service won’t start, how to fix it?
Many users reported that Windows Defender service won’t start on their PC at all. This can be a big security risk, and speaking of issues with Windows Defender, here are some similar issues that users reported:
- Windows Defender service won’t start Windows 10, 8.1, 7 – According to users, this problem can appear on all versions of Windows, including both Windows 8.1 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 ProgramData\Microsoft 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.
Solution 1 – Disable and remove third-party antivirus solutions
Running two antivirus solutions at the same time causes various technical issues. Use a dedicated software removal tools to completely remove any third-party antivirus files. Restart your Windows 10 computer and start Windows Defender again.
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, but if you’re looking for a new antivirus, we suggest you try Bitdefender.
Solution 2 – Install the latest Windows Updates
Sometimes you might be able to fix problems with Windows Defender service 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.
However, you can always check for updates manually by doing the following:
- Press Windows Key + I to open the Settings app.
- Now go to Update & Security section.
- Click Check for updates button.
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.
Solution 3 – Run an SFC scan
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. However, you can fix the problem simply by running an SFC scan. To do that, just follow these steps:
- Press Windows Key + X to open Win + X menu. Now select Command Prompt (Admin) or Powershell (Admin).
- When Command Prompt opens, enter sfc /scannow and press Enter.
- SFC scan will now start. The scan can take up to 15 minutes, so don’t interrupt it.
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. To do that, you need to do the following:
- Open Command Prompt as administrator.
- When Command Prompt opens, enter DISM /Online /Cleanup-Image /RestoreHealth.
- 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.
Solution 4 – Clean your registry
Sometimes Windows Defender service won’t start if there are issues with your registry. A corrupted registry entry can cause this issue to appear, and in order to fix the problem, you need to find and remove the problematic entry.
This is a complex task to perform manually, so it’s better to use a special software for it. There are many great registry cleaners available that can help you with that problem, but if you’re looking for a simple registry cleaner, we suggest you try CCleaner.
Solution 5 – Check your environment variables
Environment variables are a useful feature that your system uses in order to access certain directories. However, sometimes users or perhaps a third-party applications can change your environment variables and cause this issue to appear.
This can lead to issues with Windows Defender service, but you can fix your environment variables manually by doing the following:
- Press Windows Key + S and enter advanced system settings. Select View advanced system settings from the menu.
- Now click Environment Variables button.
- Locate %ProgramData% variable and check if it’s set to C:\ProgramData. If not, change the variable accordingly.
After making these changes, the problem should be resolved and Windows Defender should start working.
Solution 6 – Change system permissions
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.
To fix the problem, you just need to do the following:
- Go to C:\ProgramData directory.
- Now locate Microsoft directory and right-click it. Choose Properties from the menu.
- Now go to Security tab and click Advanced.
- Now you should remove all inherit permissions. After doing that, save changes and check if the problem is resolved.
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.
Solution 7 – Create a new user account
If 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 user account, you need to do the following:
- Open the Settings app and go to the Accounts section.
- Go to Family & other people on the menu on the left. In the right pane click Add someone else to this PC.
- Click I don’t have this person’s sign-in information.
- Now select Add a user without a Microsoft account.
- Enter the desired user name and click Next.
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.
Solution 8 – Perform an in-place upgrade
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. To do that, just do the following:
- Download Media Creation Tool from Microsoft’s website and run it.
- Select Upgrade this PC now.
- Wait while setup prepares the necessary files.
- Select Download and install updates (recommended). Wait while the setup downloads the necessary files.
- Follow the instructions on the screen until you reach Ready to install screen. 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.
- Follow the instructions on the screen to complete the installation.
Once the installation is finished, you’ll have a fresh installation of Windows and the problem should be resolved.
Not being able to start Windows Defender service can be a problem, but we hope you managed to fix this issue with one of our solutions.
Editor’s Note: This post was originally published in March 2017 and has been since completely revamped and updated for freshness, accuracy, and comprehensiveness.
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