how do I reinstall windows defender for windows 10

I cannot restart Defender--get Error 577.

Windows Defender was turned off when I installed Spybot Search & Destroy.

I don't think so - unless you turned it off.

I have tried the solution you provided above, but when I try to start the service, I get an error #577 stating that windows cannot verify a digital signature for a file.

Windows Defender was turned off when I installed Spybot Search & Destroy

Hi Lucy,

Welcome to Microsoft community.

• How did you uninstall Windows Defender?

Please follow the below steps and check:

 Step 1: Enable Windows defender from control panel 

1.    Press Windows + X, Click on control panel.

2.    On right top corner click on View and then choose large items.

3.    Now from the list click on Windows Defender and try to enable it. 

If not try to enable it from services. 

Step 2: Enable Windows defender from services.msc. 

1.    Press Windows + R, to open run prompt.

2.    Type services.msc and press enter to open services list.

3.    Under services look from Windows defender service and start the service.

If you face any issue while troubleshooting, please provide the outcome, so that we can work on your issue. 

Hope the information helps, if you have any further queries, feel free to post. We are here to assist you.

Rehards,

Guru Kiran

Dear Mr. Guru Kiran,

Your info was highly helpful.

however I'm facing an different issue! I'm not able to update my windows defender.

So can you pls help me out for this?

Awaiting your valuable response.

Thanks

Nambi

Can not find Windows Defender to reactivate. How do I reinstall?