how do I reinstall windows defender for windows 10

Well I installed Malewarer bites and that cleaned up all malewhere I had but have corrupted files still so Windows Defender still not working,How ever a friend of mind who is a computer expert mentioned that I should reinstall Windows 10 to compleately clean out hard drive and problems. I can always reinstall what ever like e-mail and pictures and have seen this option in tools so might just do that. Thanks for the answer.

You cannot have two antivirus apps working at the same time, it will end in a punch-up as to which one should be in charge.

Windows Defender is not a separate app to Win10, it is integral and as such the whole thing needs mending.

I remind you of my post 29th June 2016 in this thread.

Use the antivirus removal tools supplied on line by third party antivirus apps, externally back up your data and apps you want to keep and use win10 internal recovery. I would suggest using the "keep your data and apps" option first. The beauty of using the "delete all" option is a clean start though you will need to re-enter your apps as well as data. If that don't work send the damn thing to a computer doctor.

PS. Try and get your emails on your providers email page or cloud so you can re-download as necessary.

Regards and a happy Christmas

I know that you can do that but first you have to disable all other antivirus applications

what I was asking if you can have window defender and lets say Norton antivirus,so I can go back to

using EDGE as a web search

Norton does not support EDGE  and windows defender by itself is not enough protection

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

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

Running Spybot and Windows Defender – Windows 10

https://www.safer-networking.org/faq/spybot-defender-windows-10/