Never got Windows to boot again, just had to wipe and re-install
So I was never able to get my Bootcamp Windows 8.1 install to boot again or get it to repair, so i finally just used. Bootcamp Assistant to wipe the partition, and re-partition.
Now I ended up having to do this 7 times, as 6 times windows on it's first restart it came to an error message loop saying "The Computer Restarted unexpectedly or encountered an unexpected error. Windows installation cannot proceed. To install Windows click OK to restart the computer, and reinstall Windows." I finally found a fix for this ( https://avatargamingpc.com/support/951869-The-Computer-Restarted-unexpectedly-or-encountered-an-unexpected-error-during-installation-of-Windows ) but the Windows install had totally tanked by that time, and on the next re-partition and re-install, the install actually worked.
Have spent the day upgrading, and am now installing 8.1. Then time to re-install everything, and make a backup disc!
What a pain in the ass!