If Windows Defender does not start, you can resolve it through the following steps: 1. Uninstall third-party antivirus software to avoid conflicts; 2. Use the system's own troubleshooting tool to automatically repair it; 3. Turn on the service manually or change the DisableAntiSpyware value in the registry to 0; 4. Update the system or reset the Defender through PowerShell. Trying in sequence usually solves the problem without having to reinstall the system immediately.
It's really a headache to not start Windows Defender, especially if you know it's important to system security. Don't worry, this situation is actually uncommon, and most of the time it can be solved in a few simple steps.

1. Check whether there are third-party antivirus software conflicts
Many users will find that Windows Defender is automatically disabled after installing other antivirus software (such as Kaspersky, Turfur, 360, etc.). This is because Windows system only allows only one antivirus program to run by default to avoid conflicts.

- Open Settings > Apps > Apps and Features
- Find out if there is any installed antivirus software in the list
- If so, try uninstalling them, and then restarting the computer to see if Defender can recover
If you just want to use Defender temporarily, you can turn it off or uninstall third-party software killing first.
2. Use the system-owned troubleshooting tool
Microsoft has already taken this into consideration, so it provides a gadget for automatic detection:

- Open Settings > System > Troubleshooting
- Find "Other Troubleshooting" or search directly for "Windows Security Center"
- Run related diagnostics and the system will automatically try to fix some common problems
This method may not necessarily solve all situations, but it is simple and fast, and it is worth a try.
3. Manually enable the service or modify the registry (advanced)
If the above methods are not available, it may be because the Defender service has been closed or the registry key has been changed.
Method 1: Check the service status
- Press
Win R
and enterservices.msc
to enter - Find
Windows Defender Antivirus Service
- Right-click to select "Properties", change "Startup Type" to "Auto", and then click the "Startup" button
Method 2: Check the registry (operate with caution)
- Press
Win R
and enterregedit
to enter - Positioning path:
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender
- Check if there is an item named
DisableAntiSpyware
on the right. If the value is1
, it means it is disabled. - Change its value
0
and restart the computer
This step has a little technical threshold. It is recommended that friends who do not understand the registry should operate with caution, or find someone who understands it to help.
4. Update the system or reset the Defender
Sometimes the problem is that the system file is damaged or the Defender component itself is broken.
- Make sure your system is up to date, open Settings > Update & Security > Windows Update to check for updates
- If the update is not useful, you can try resetting the Defender:
- Open PowerShell (Administrator permissions)
- Enter the following command and press Enter:
Add-MpPreference -ExclusionPath "C:\Program Files\Windows Defender"
- Or try reinstalling the Defender module (need to be connected to the Internet)
Basically these common ways of dealing with it. Some are simple checks, while others require a little hands-on ability. When you encounter problems, just do it step by step and don’t rush to reinstall the system.
The above is the detailed content of Windows Defender won't turn on. For more information, please follow other related articles on the PHP Chinese website!

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