Open Task Manager (Ctrl + Shift + Esc)
Click File - Run new task
Tick the box marked 'Create this task with administrative privileges'
Type powershell into the box and click OK
Run this command and press Enter:
Get-AppxPackage Microsoft.Windows.ShellExperienceHost | reset-AppxPackage
When that completes, run this command and press Enter
Get-AppxPackage Microsoft.Windows.StartMenuExperienceHost | reset-AppxPackage
When that command completes, restart (not shut down) your PC.