Arc, try this. Create a restore point first!
Elevated PowerShell, you need first unrestricted script execution rights, command is:
Then re-register the Store:
Close the PowerShell, the store should work now. If it will not start, give this command in Command Prompt (not PowerShell!):
Add-AppxPackage -DisableDevelopmentMode -Register $Env:SystemRoot\WinStore\AppxManifest.XML
Come back to tell if we need to try something else or if this worked.
start "" "ms-windows-store:"