Sebastian42

'use a USB enclosure for an instance where I don't want to have the disk connect at boot time.' That sounds to me like it might work. I'll try it as soon as I can.

"what you really need is a way to boot the PE at a time when the normal "system" disk is connected." - I would gladly settle for that. "settings in BIOS (or UEFI) that allow booting from an external disk (USB) with the internal disk(s) normally connected." Lacking that seems to be the root of my problem. I have only chosen 'boot-from-USB' in the Boot sequence, not in the actual BIOS settings - I KNOW of an option there, but have not yet tried that. I wont list the mobo code yet Booting from BIOS. "have you tried re-scanning with diskpart or devcon [1] after having connected the disk?" No, and never heard of devcon. My post has been severely interupted and other things are going wrong, so I will just post this now, and look at it again tomorow

I've been persuaded that WinPe is the way to get the required 'authority' to alter registry keys that resist change. The registry is obviously on a drive and so WinPe must 'see' drives to be able to alter their registry. I managed to get a bootable USB which launches WinPe. It has a THIS PC option, but when that is opened, connected drives do NOT show. (How) can that be remedied ? PS WinPe DOES see other drives - ones that were already connected when WinPe booted; I can't connect the system drive - whose registry I want to change - before booting WinPe, because then the PC boots from the system drive rather than from the WinPe USB.