Windows 10 Taskbar/Startmenu/Notifications not working

• Symptoms (Windows 10):

  
  
  
  
  • Startmenu & Notification area won't open
  
  
  • Right click on any of the icons in my taskbar doesn't do anything
  
  
  • Many Windows apps don't work
  
  
  • The "Loading" cursor flashes like crazy from time to time (especially when trying to interact with the taskbar)
  
  
  • Adding a different user account seems impossible:
    
    
    
    • CMD: adding a user works fine, however I cannot log into the account
    
    
    • UI: adding a new user doesn't work at all. A window opens and closes again.
    
    
  
  
  • The Microsoft Taskbar troubleshooter detects the following problem, however seems to be unable to fix it (even when run as
    administrator):
  
  

"Microsoft.Windows.ShellExperienceHost" and "Microsoft.Windows.Cortana" applications need to be installed correctly.

• I have already tried:
  
  
  
  • Adding a new user account
  
  
  • Some user (who had the exact same problems) fixed it by setting a
    different default monitor, however I don't have a second monitor and
    I never had one, so this should not be the cause
  
  
  • Deleting C:/Users/name/AppData/Local/TileDataLayer
  
  
  • Repairing windows
    
    
    
    • running sfc /scannow
    
    
    • running dism /online /cleanup-image /scanhealth
    
    
    • running dism /online /cleanup-image /restorehealth
    
    
    • reparing the system via CTRL+ALT+DEL -> SHIFT + Restart -> repair didn't work either.
    
    
    • this ps script:
    
    
  
  

Get-AppXPackage -AllUsers | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"}<

Get-appxpackage -all shellexperience -packagetype bundle |% {add-appxpackage -register -disabledevelopmentmode ($_.installlocation + “\appxmetadata\appxbundlemanifest.xml”)}

Get-AppxPackage Microsoft.Windows.ShellExperienceHost | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"}

Get-AppxPackage Microsoft.Windows.Cortana | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"}

If you have any idea how to fix this, please help.

Answer

Tweaking.com has a nice program called "Windows Repair" (http://www.tweaking.com/files/setups/tweaking.com_windows_repair_aio_setup.exe), which was able to solve the issue for me. I still don't know, what caused it.