Apps Store Cannot Open In My Windows 8.1

The following finally fixed all issues for me (Store and all apps broken with black X, can't access PC Settings):
1) Fixing the app store:
1. Open registry editor typing regedit.exe from a command line.
2. Browse to the registry key at HKEY_CURRENT_USER\Software\Classes\Local Settings\software\microsoft\windows\currentversion\appmodel\repository\packages.
3. Right click on the “packages” key and bring up the “Permissions” tab.
4. Click the “Advanced” button located at the bottom right corner.
5. Check to see the account name that shows up as the “Owner” (this is the first line of text on the “advanced security settings” dialog for the “packages” key). It should say “SYSTEM”. (For me this showed the built-in local Administrators group)
6. If it is any other account, click on the “Change” button next to it.
7. Type SYSTEM in the “select user” dialog. If “Multiple Names Found” window comes up, select the row for “SYSTEM”.
8. Click OK to the dialogs and close them all.
9. Run from admin command prompt: Powershell -ExecutionPolicy Unrestricted Add-AppxPackage -DisableDevelopmentMode -Register $Env:SystemRoot\WinStore\AppxManifest.xml
2) Fixing all modern apps:
Run from admin PowerShell:
((Get-ChildItem "HKLM:SOFTWARE\Microsoft\Windows\CurrentVersion\Appx\AppxAllUserStore\InboxApplications") | Get-ItemProperty).Path | Add-AppxPackage -Register -DisableDevelopmentMode
* When I ran this the black X persisted until after the next step and reboot. But trying to start an app gives me a new message and a link to the store.
3) Fixing 3rd party apps:
Delete the regkey: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Appx\AppxAllUserStore\[UserSid]
4) Restart. After a reboot the apps still showed the black X for a minute or so, but it soon cleared up on its own and all apps seemed to be working again. I was also able to update the apps from the app store once signing in with a Microsoft account. Finally, I am again able to get into PC Settings.

Hope this helps

---

Tech freak