Shawn - thank you for all the great tutorials down through the years both here and at Seven Forums. They've been enormously helpful.
I
really think you should make the Data disk focus explicit in the thread title and add a warning at the top reinforcing that the various covered approaches are for Data disks only and using them on an OS disk is high risk and can result in not only a non-bootable computer but also a
non-recoverable boot drive without access to an alternate boot mechanism (like bootable recovery USBflash drive).
I used the MiniTool Partition Wizard approach (the free version of the EaseUS tool does not support GPT to MBR). Like @
anctop I attempted to convert an OS drive. As stated above making partition changes to the boot partitions must be completed between the Starting Windows and Welcome/Login steps in the boot process. In my case (like for anctop) it resulted in a boot error with "No OS found message" when restarting.
I wasn't as smart as anctop so when I got that message instead of setting the boot partition to Active with diskpart I tried to revert to a bootable state (I use Macrium Reflect) with following progression:
- attempted to restore the most recent verified backup (a fresh updated/activated install) with GPT scheme: on restart got the two blinking cursors but boot would not progress to Starting Windows
- attempted to restore a Win7 MBR image: on restart got the two blinking cursors but boot would not progress to Starting Windows
- used the Reflect recovery capability to Fix Boot Problem: despite a Successful Update of boot files message the system would still not progress to Starting Windows
I've never had a disk image restore fail to result in bootable condition. I've done a bit of experimentation in my OS (in the MBR world) but always with the confidence that reverting to a stable bootable state was only an image restore away; suffice to say this was quite a nasty surprise.
The fix was to boot using the Win10 recovery Toolkit USB and Clean the disk using diskpart so the entire disk was unallocated. After that the Reflect restore worked as advertised.
Certainly this appears to be a problem with Reflect's restoration process but it illustrates how badly things can go awry if the GPT to MBR conversion process is applied to a live OS.