Windows Defender turns off immediately after turning on (Win10)

I have kinda a big problem.  I uninstalled Bitdefender as my old antivirus, and I wanted to use Windows Defender in the meantime while I looked for a different Antivirus.  Problem is, I can't turn it on.  I get a screen like this:

Naturally I press start now (or turn on depending on the screen presented to me)

Then it's fine for a few seconds.  After those few seconds pass, it goes right back to the old screen:

I can't figure it out for the life of me.  I tried doing the sfc scannow command and it said it was unable to fix some corrupted files or something (maybe that's it?).  Anyways, I don't get this.  It just keeps turning off as soon as I press turn on (or in this case "start now").  I'd appreciate help because this is bugging me and does not seem good.  

Also I get this when I try opening the app directly:

I uninstalled Bitdefender without much of a trace and restarted several times, but still nothing.  


Question Info

Last updated March 17, 2019 Views 2,528 Applies to:

The behavior you are describing is typical if there are remnants of a third party program installed that are interfering with Windows Defender.

Did you follow the steps recommended at

What program did you use on the computer before BitDefender?  AVG, McAfee, Norton?  Try running the removal tools for any security program that you previously used on the computer: List of anti-malware product removal tools 

Go to Security and Maintenance, look in 'Security' and see what program is listed under Virus Protection.  Windows Defender will not be enabled if there is a program other than Windows Defender listed.

Have you tried the steps recommended in Problems starting Windows Defender in Windows 8/8.1/10?


For further information see the reply of quietman7 in this thread:

The inability to turn on Windows Defender 8/10 is typically the result of having a third-party anti-virus installed or failure to remove it properly (completely). Since Windows 8/10 Defender includes anti-virus protection, it is disabled during the installation of another anti-virus program. If a trial anti-virus (i.e. McAfee, Norton, etc) came preinstalled on your computer or you installed one, Windows Defender will be turned off (disabled). Windows Defender recognizes the install and automatically disables itself when other anti-virus products are used to avoid conflicts. Windows Defender will remain disabled until that anti-virus software has been completely uninstalled. In some cases, you may need to download and run the anti-virus vendor's clean up tool to remove any remaining remnants.

After removal of the third party anti-virus, Windows 8/10 Defender needs to be activated if you choose to use it. When uninstalling the third-party anti-virus Defender should automatically turn itself on but sometimes you may receive a message indicating 
your system has no here to turn on Windows Defender. If not, and Defender remains disabled, you will need to manually turn it on.

If that is not the case in your situation, check to make sure the Windows Defender service is started.

Sometimes it may take a couple of computer reboots after performing the above steps to ensure Windows Defender is up and running properly.


Or - - -

There are a number of viable antivirus options available for Windows 10 – free or paid - take your pick…

Choosing an Anti-Virus Program

Is Windows Defender The Best For Windows 10?  Good article but ignore the ads.


MVP Consumer Security 2014-2016
Windows Insider MVP 2016-2018

1 person was helped by this reply


Did this solve your problem?

Sorry this didn't help.

Great! Thanks for marking this as the answer.

How satisfied are you with this reply?

Thanks for your feedback, it helps us improve the site.

How satisfied are you with this response?

Thanks for your feedback.