running Windows 10 build 10166. working fine until this morn, last major thing i did was upgrade iTunes (hardly major!). now start menu is gone, icon is there, just no start menu. action center wont open either and unpin option is gone from taskbar icons.

have tried...

(1) changing user accounts. wont let me. click the + icon in user accounts and nothing happens.
(2) tried the powershell trick, running as admin and pasting in Get-appxpackage -all *shellexperience* -packagetype bundle |% {add-appxpackage -register -disabledevelopmentmode ($_.installlocation + \appxmetadata\appxbundlemanifest.xml)} . nothing happens even after a restart
(3) tried system restore. usually a lifesaver, but this time it only showed 2 restore points from hours earlier, neither worked and one from yesterday has vanished.
(4) tried sfc /scannow, says there are corrupt files but cant fix them automatically. (and the log file it generated is gibberish to me).
(5) tried safe mode. still no start menu etc.

any ideas/help is much appreciated!