the ‘staged’ installation of KB2929355 has been superseded by a failed installation.
Did your list of installed packages change too? I think you can use Powershell in the Command only boot.
So I tried booting from my Win 8 recovery disk. It says the drive where windows is installed is locked. But dropping to a command prompt reveals that the drives have all been remapped! The SSD normal boot disk is E: and my old system disk is C: (which now only has data on it). There doesn’t seem to be any way I can tell recovery to look at E: to refresh it.
I don't think you have to worry about the letters. That seems to be normal, especially when you are booting from a different drive. I don't think it is normal for the install drive to be locked though. I imagine that diskpart has a way of "unlocking" it but I'm not sure of the details. Please don't do anything drastic. I had one user misinterpret my suggestion to use diskpart as a diagnostic to somehow cause it to format the drive.