Which version do you have of Windows Defender? You might want to consider uninstall than
Download install and update
CcleanerAfter installing and updating go to options - advanced and tick prompt for registry back ups
Now
Start up in safe modeDo two runs
1) Click on problems and tick all. Click on analyse. At the end you will be prompted for storing a backup.
This will be stored, as a default, in My documents.
2) Click on cleaner click on analyse and accept all files to be removed.
thiswill remove any traces of WinDef in the registry
than re-install and you should be fine