Hi, I am Dave, I will help you with this.
1
Download this file from the Microsoft Catalog.
https://catalog.s.download.windowsupdate.com/c/...
Run that file, a Command Prompt window will open and then close after a couple of seconds.
Restart (not shut down) your PC to apply that change.
Then check if Windows Security is working.
2
If that does not resolve the problem:
Click your Start Button, then just type Powershell and on the resulting list, right click PowerShell and select 'Run as Administrator'.
Paste this command into Powershell and press Enter:
Get-AppxPackage Microsoft.SecHealthUI -AllUsers | Reset-AppxPackage
When that completes, paste this command into Powershell and press Enter:
Add-AppxPackage -Register -DisableDevelopmentMode "C:\Windows\SystemApps\Microsoft.Windows.SecHealthUI_cw5n1h2txyewy\AppXManifest.xml"
Close PowerShell and restart (not shut down) your PC