Start menu and settings won't open

Hi,

So all of a sudden my start menu won't open and neither will settings.
This seems to have roughly coincided with a "critical update"

Left clicking on the start menu simply doesn't work. Right clicking
usually works (to open the right click menu). Oddly, sometimes a
combination of left and right clicking in succession will open the start
menu properly.

Settings will also not open, I've even tried ms-settings: in the run box
but get nothing. Things I have tried so far to rectify the problem
(unsuccesfully)

- System restore (this has only let me go back a few hours to the last
critical update)
- Running System File Checker from elevated command prompt
- Repairing Windows Image from elevated command prompt

I'm regularly restarting as part of my efforts to solve this problem and
this has thrown up a new problem - "Task Host Window" stopping the PC
from shutting down. In an attempt to try to resolve this (could it be
related?) I have tried disabling fast start up but this hasn't helped.

I've also tried booting in safe mode with networking and then the
problem goes away so there must be some solution.

What next???

Thanks!