I HAVE SLAIN THE BEAST!
I was able to get it by the following commands...
First, in my last post, I did (with cmd Run as Administrator)
Dism /Online /Cleanup-Image /RestoreHealth
Then, I found another command,
Dism.exe /online /Cleanup-Image /StartComponentCleanup
I then ran
sfc /scannow
and then finally, I ran
Disable-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V-All
in PowerShell (running as admin).
I am not sure if I had followed that order with Visual Studio still installed, that I would have got it. Nonetheless, I have the ability to run 64bit VM's in VirtualBox because Hyper-V is disabled. I think that there was just enough wrong with my Windows install that it needed these commands, after I ran sfc it said it had found some errors and corrected them. I believe the order isn't perfect either, but this is what worked for me. Thanks to all for your help.