Long story short, windows 10 is utterly broken on my laptop after it automatically installed some updates. It's now stuck in a loop which always ends up saying "Undoing changes made to your computer"
I can't get into the BIOS.
I can't get into the Windows Recovery Environment.
Been talking to MS support for far too long so far, so I'm wondering if it's possible to add it as a secondary disk drive to another machine that does work, and manually remove any updates that were installed directly through the filesystem?
The only solution MS were willing to offer was to format the whole drive and re-install windows.
When I moved the HDD into a working windows 7 machine it actually prompted a chkdsk to run over the disk.
It found a whole load of orphaned files, not sure if that was really the cause, but after backing up as many files as I had access to, I put the drive back into the other machine and now it boots.
tl;dr, chkdsk fixed it.