Windows 10: Unable to start Windows Defender service

My Defender service has stopped working. Description of behaviour is below.


In the security settings, it says the service has stopped. There is a button to restart but clicking it returns an error message. Unexpected error, it appears there is a problem, try again later :




Trying to start in Computer Management also returns an error : Cannot start the service, error 87 incorrect parameter :




A related symptom is that opening the security settings gives a message about the administrator allowing limited access, contact IT helpdesk : (note this is personal windows 10 at home, not in an organisation !) :



Another symptom is that virus definition updates don't seem to install. The update will run (showing up to 66% complete) but will then quit. (Windows Update works fine for other components.)



There is no third party antivirus software on my system, although I recently did use Malwarebytes. (Actually I suspect a recent virus has messed up Windows Defender, but not sure.)

I have tried some fixes found online but no success. Please advise ?

:)

 

Windows Defender disabled and is unable to start


OK. I am not sure if you can complete the steps below.......................
In the search box, type services.msc > Enter
Items in the Services box are listed alphabetically.
Scroll down to Windows Defender Service...........................
at Status heading, it should be.................................... Running
at Startup type, it should be......................................... Automatic







If that is not what yours said, right click at Windows Defender Service > click Properties >
can you change the Startup type to Automatic and Service status to Start ?
If yes, do so and click OK when done.

 

Unable to Re-Start Windows Defender Services


A little background first, I downloaded a file and started to install it when Defender caught the virus, but didn't contain it. So I downloaded Malwarebytes to scan and remove the virus.

After I loaded Malwarebytes I noticed I wasn't getting anymore Windows Defender definitions but I noticed the Windows Defender services were stopped and I figured Malwarebytes stopped it and that was the reason I wasn't getting anymore updates on Defender.

I uninstalled Malwarebytes but now I can't restart Windows Defender.

If I got to Control Panel then Security and Maintenance window. Both buttons to turn on Defender are grayed out.





If I search for Windows Defender in the search window on the task bar. This is the result I get.





And lastly, if I go into Task Manager Services, there are 2 entries for Windows Defender, both are stopped. If I try to restart them this is the message I get.





So is there anything I can do to restart the app or does it require more drastic steps such as reload 9926?

 

Windows Defender disabled and is unable to start


Hi guys!

I finally managed to fix my Windows Defender. I had to restore the service using registry key. And also make changes in the registry using steps mentioned on articles online.

I restored the WD default registry key through the steps provided here this restored my service of Windows defender.

Services - Restore Default Services in Windows 8

It seems that the registry key for WD of Windows 8.1 is same as that of Windows 10.

I also followed the steps mentioned here:
[FIX] Windows Could Not Start The Windows Defender Network Inspection Service On Local Computer

And

Here:

Windows Defender Does Not Start in Windows 10 - WindowsInstructed

So far it's working fine. Will report back if I see anything weird pop up as I did fiddle with the registry keys.

Thanks for the help davidhk