Long and painful process to be honest. I expect this would be a very rare occurrence, it was only due to the fact I broke things a year ago and never noticed. Almost all of this was done booting from...

Found the cause of my 80070003 error: I had no MSR or EFI partition. I changed disks about a year ago and I guess things were broken for this whole time. After this was resolved I was able to upgrade...

I haven't figured this out just yet but I agree it's disk related.

FYI:
msconfig -> Boot.
There are no entries
Control panel -> Advanced system settings -> Start-up and Recovery settings
...

I have the exact same symptoms as Snaiper.
chfslt, my disk looks like this. I have only one Windows host so nothing to compare to

Also note I'm using mirrored root disks

DISKPART> list disk
...