Fix Store App in Windows 8.1

• Sometimes, after upgrading to Windows 8.1, the Store App may not start.
• It might still show the number of available updates on the Live Tile.
• Starting the app may show a progress ring but it may not finish loading.

• To fix this, run the following in a Command Window (CMD) to re-register the Store App:

powershell -ExecutionPolicy Unrestricted Add-AppxPackage -DisableDevelopmentMode -Register $Env:SystemRoot\WinStore\AppxManifest.XML

• If you get error 0x8007064A after executing this, it means that the registry key "HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\CurrentVersion\AppModel\Repository\Packages" does not haveSYSTEM as the owner.
• Change the owner back to SYSTEM as explained here and try again.

• To fix three other system apps such as PC Settings, run the following:

powershell -ExecutionPolicy Unrestricted Add-AppxPackage -DisableDevelopmentMode -Register $Env:SystemRoot\camera\AppxManifest.xml

powershell -ExecutionPolicy Unrestricted Add-AppxPackage -DisableDevelopmentMode -Register $Env:SystemRoot\FileManager\AppxManifest.xml

powershell -ExecutionPolicy Unrestricted Add-AppxPackage -DisableDevelopmentMode -Register $Env:SystemRoot\ImmersiveControlPanel\AppxManifest.xml