I recently moved to Windows 8.1 and experienced a strange problem where some windows would not open (PC Settings, Bluetooth Settings etc).
This article fixed it for me:
Simply enter this Powershell code into a command prompt and presto! No restart required…
powershell -ExecutionPolicy Unrestricted Add-AppxPackage -DisableDevelopmentMode -Register $Env:SystemRoot\ImmersiveControlPanel\AppxManifest.xml
