Here's an update from my side.
I installed Classic Shell for Windows 8, which thankfully makes the computer useable again.
If I run OD2.1 now, and click the Start button on the dock, the Classic Shell Start menu pops up - which is exactly what I want! Whoopee!
However, if I then select the "Hide task bar" option on the OD2.1 settings and click Start this time, nothing happens (actually there's a brief flash of the start menu, but then it disappears instantly). I suspect OD2.1 is somehow suppressing the Classic Start menu from popping up.
I don't want to run with both the OD2.1 dock and the Windows task bar showing because that would be silly.
Any thoughts?
I'm guessing not many people use OD2.1 with Windows 8 because this is a very obvious requirement.
Cheers,
Geoff