Keeping the Windows Defender enabled is crucial, especially if you don’t have another antivirus on your PC. However, the Windows Defender sometimes fails to start, leaving your machine defenseless. If you are here, you have probably tried restarting your computer and other tricks, but that didn’t help. Well, you’ve come to the right place. Today’s post will explain how to solve the Windows 10 Defender won’t turn on issue.

What Causes This Error on Windows 10 PCs?

Windows Defender is likely to fail on launch due to the following reasons:

  • Outdated operating system
  • Wrong date and time
  • Third-party antivirus apps
  • Registry issues

How to Solve Windows Defender Service Won’t Start

Since varying factors trigger this error, we suggest you try different tactics until the problem disappears. Below are the techniques that proved effective on most people’s devices with the same issue.

Method 1: Check Your Date and Time

Did you know that many PC apps usually depend on the system date and time to perform some functions? Therefore, if these are incorrect, you could easily experience abnormal behaviors with some programs. Thus     , ensure you check if your device reads the correct date and time. If not, correct it immediately and then check for the issue.

Method 2: Disable Your Third-Party Antivirus App

Antivirus apps usually work differently. Some can work without interfering with other programs on your computer, while others can’t. If you have an invasive antivirus app, it could be the trigger. Therefore, open the app’s settings and temporarily disable its protection. Then reboot your computer and check if Windows Defender will launch. If it does not, try uninstalling the third-party app to see if that helps.

We also recommend installing a professional antivirus program that can protect your computer without interfering with other system functions. A good example of such an app is Auslogics Anti-Malware.

Method 3: Update Windows

Windows is an amazing operating system, but it sometimes gets buggy, triggering issues such as Windows Defender not working correctly. Installing the latest updates is the best solution. Windows can download updates in the background. However, if you have disabled updates on your computer, you might have missed some.

Follow these steps to update your operating system:

  1. Launch the Settings app by pressing Windows Key + I on your keyboard.
  2. Go to Update & Security.
  3. Click on the “Check for updates” button.
  4. Wait for the system to check for updates and download them on your machine.
  5. Once done, restart your computer.
  6. Now check if the problem has been fixed.

Don’t give up if you are still getting the error when trying to open Windows Defender. The following tip might help.

Method 4: Use the System File Checker SFC

File corruption is a common cause of most issues on Windows PCs. So, it could also be why you can’t successfully launch Windows Defender on your machine. Luckily, the System File Checker can help scan your computer for corrupted system files and immediately repair them.

Here is how it works:

  1. Press the Windows logo key + S combination to bring up the search bar.
  2. Type in “command” (without quotes) and then right-click on Command Prompt.
  3. Select Yes if the User Account Control (UAC) prompt appears.
  4. When the command prompt window opens, type in “sfc/scannow” (no quotes), then hit Enter.

Try using the System File Checker (SFC)

  1. The SFC tool will automatically scan for corrupt and damaged files and repair them.
  2. Restart your PC once the process completes.

Method 5: Change the Registry Settings

Some users also said that tweaking their registry settings helped fix the error. You could try doing the same to see if that helps. However, the registry is pretty sensitive. So, messing up crucial keys could easily damage your computer. Therefore, we suggest that you back up the registry before moving further. Doing so will enable you to easily reverse any mistakes and restore your PC’s health.

Follow these steps to back up the registry:

  1. Press the Windows Key+ R combo to open Run.
  2. Type in “regedit” (without quotes) and click the OK button.
  3. Click on the Yes button when the UAC window pops up.
  4. Select “File” in the upper-left corner of the Registry Editor. Then choose Export.

Tweaking Windows registry settings may help fix Windows Defender won't start issue

  1. Select where to store the backup file and then name it.
  2. Finally, click on the Save button.

Now use this quick guide to tweak your registry settings:

  1. Open the Run dialog box (Win + R).
  2. Type in “regedit” (no quotes). Then hit enter.
  3. Choose Yes on the UAC prompt to open the Registry Editor.
  4. Navigate to the following path:

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender

  1. Once here, find “DisableAntiSpyware” on the right pane. If you can’t locate it, right-click on the right pane, choose “New”, and select “DWORD (32-bit) Value”. Name this file “DisableAntiSpyware”.
  2. Now right-click on “DisableAntiSpyware” and select Modify.
  3. Change the Value data to “0” and click on the OK button.

Use this guide to tweak your registry settings

  1. Close the Registry Editor and reboot your machine.
  2. Check if this technique worked.


The cannot start Windows Defender error message is quite annoying but not unfixable. This article has discussed the different ways you can go about it. Therefore, we hope that this error is no longer an issue on your Windows PC. However, if you still have any unanswered questions regarding today’s topic, drop them in the section below.