Windows Defender

Windows Defender wont open after Creator update.

How are you trying to open it?
If from the icon in the tray, right click > open
or
All Settings > Update & Security > Windows Defender > Open Windows Defender Security Centre

Which 'Defender' are you trying to open? Double-clicking on the Defender icon in the notification try does nothing. This seems to be a design oversight, but right-click brings up 'Open' which opens the Windows Defender Security Center.
Open Windows Defender Security Center in Windows 10

The old style Defender is still available if you really want it, but takes about a minute to open. Run (or make a shortcut to)...
C:\Program Files\Windows Defender\MSASCui.exe

Which 'Defender' are you trying to open?

How many are there?

Clint said:

How many are there?

The old UI you're used to from previous versions, and the new Defender Security Center in the Creators Update. There's just the one Defender service running, but there's two ways to see what it's doing and control it, the old way and the new way.