Start Menu, Cortana and most Metro Apps/UI features fail to load

Hi,
I've become a victim of the "Critical Error - Your Start menu isn't working. We'll try to fix it the next time you sign in" error. The Start menu prompts this error to appear, while Cortana, Battery, Wireless, Sound, Notifications and Clock also do not respond to clicks; and Metro apps also do not work (notably, Task View still works). This has been ongoing for about 2 to 3 months, interrupted by two days in which it all worked following an upgrade, but fell back to the error shortly after.

The only Metro App I can get running is Settings (may not be Metro) which works 98% of the time when Right Click>Display Settings is used. 2% of the time it says something like "You need a new app to open this file: ms-settings".

The obvious response to this was to perform an Upgrade in Place. I decided not to follow it through when it told me I would lose all my files because "your current version of Windows might be installed in an unsupported directory". Following a reddit guide, I saw that this refered to a registry key dictating the location of Program Files and Users; but having not ever editted these keys, or ran any programs that would have needed to edit these keys, I opened regedit and confirmed these keys were default.

System file checker returned no errors.

Having nothing to lose, I then proceded to run every reputable fix for this issue under the Sun. From reloading apps with dism, to deleting drivers in safe mode and registry hacks and new accounts; the only hope was when I briefly got a blank start menu, though a reboot quickly ended that. I beleive dism made the situation worse, as when running it, the Powershell window steadily filled up with red errors and ended with a Taskbar void of any Metro apps.

I have already done a complete reinstall of Windows due to a very similar issue in the past year, and see no reason for doing another immediately when it will likely ultimately end in the same results.

If anyone has a solution/suggestion, or a similar issue, please share it!

Many thanks.