Right I had this issue after migrating a system image from a VM to my phsical laptop.
First thing to try is the System File Checker – Run this as admin. If you can’t get CMD open, remember its located at c:WindowsSystem32. You could get here by CTRL+R > Type the location > Hit Enter.
sfc /scannnow
If the outcome says that it could not repair the files, either mount the windows 10 ISO or insert the disc and then run this:
Dism /Online /Cleanup-Image /RestoreHealth /source:WIM:F:sourcesinstall.wim:1
F = the drive letter the media is mounted to.
Then re-run sfc /scannow
If this failes, run PowerShell in admin mode (can be found at C:Windowssystem32WindowsPowerShellv1.0)
Get-AppXPackage -AllUsers | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register “$($_.InstallLocation)AppXManifest.xml“}
At this point my start button and system tray started to work again.