I have also run the apps.diagcab tool multiple times. It tells me my display adapter drivers might need to be updated (they don't) and and also tells met that it did a "Check for missing or corrupt files" which it says it detected every time. I have run
it and rebooted multiple times. I'm not running any anti-virus other than Windows Defender. I had Stardock's ModernMix running in Window 8 before the upgrade. I thought it might be causing an issue so I uninstalled it. Issue still existed. I haven't done anything
else to the system other than running some Windows Updates.
Guys, i've FINALLY found an answer to how to get this to work again, (courtesy of andy562)! Andrés this may work for you too.
The following finally fixed all issues for me (Store and all apps broken with black X, can't access PC Settings):
A.) Fixing the app store:
Open registry editor typing regedit.exe from a command line.
Browse to the registry key at HKEY_CURRENT_USER\Software\Classes\Local Settings\software\microsoft\windows\currentversion\appmodel\repository\packages.
Right click on the “packages” key and bring up the “Permissions” tab.
Click the “Advanced” button located at the bottom right corner.
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)
If it is any other account, click on the “Change” button next to it.
Type SYSTEM in the “select user” dialog. If “Multiple Names Found” window comes up, select the row for “SYSTEM”.
Click OK to the dialogs and close them all.
Run from admin command prompt: Powershell -ExecutionPolicy Unrestricted Add-AppxPackage -DisableDevelopmentMode -Register $Env:SystemRoot\WinStore\AppxManifest.xml
* 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.
C.) Fixing 3rd party apps:
Delete the regkey:HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Appx\AppxAllUserStore\[UserSID]
You can find your SID by going to an elevated command prompt and typing
wmic useraccount get name,sid
D.) 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.