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