Question UEFI dual boot 2x WIN 10 Pro failing

Jan 11, 2021
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Dear all,
I ll be the first to admit that I have created this mess, but now got so far stuck that I can't find a way out anymore. Any help is very welcome!

What I did:

  1. I started with 2 perfectly running win 10 pro installations on 2 different drives ("Work" drive and "Play" drive), with every restart ending up at the WIN 10 UEFI Dual Boot Screen.
  2. Then I decided to reinstall the "Play" drive, so I deleted all partitions on this drive and installed WIN 10 Pro through my USB drive created with the Windows Media Creation tool.
  3. I now believe that this drive originally contained the Boot sector and had a GTP table.
  4. Upon restart I could only boot into the new "Play" drive, which was now in MBR table (MB is set to UEFI + CSM mode).
  5. I manged to rebuild the Boot sector on the "Work" drive with bootrec /FixMbr bootrec /FixBoot bootrec /ScanOs bootrec /RebuildBcd. Which allowed me to boot to both drives, but only by going into the boot menu (F12), so no DUAL Boot Screen.
  6. Running Diskpart I noticed that now both drives were in MBR. Thinking this might be an issue I converted both to GTP with the win 10 MBR2GTP commands.
  7. This didn't change anything either. On restart I didnt get any DUAL Boot screen and could only get to the "Play" drive by going into the Boot menu, or changing the Boot order in the BIOS.
Now the real mess started:

  1. I then decided to install EasyBCD on the "Work" drive and added the to bootable drives. This worked ONCE. On restart I got the UEFI Dual boot screen and booted to the "Play" drive.
  2. Restarting from the "Play" drive however got me straight back to the "Play" drive and restarting from their did the same without any dual boot screen.
  3. Then I thought I ought to install EasyBCD on the "Play" drive as well, which I did.
  4. This resulted in No dual boot screen and trying to boot to the "Play" drive I got a “No windows installation found”
  5. Now desperate I ran an auto-repair from Easy Recovery Essentials on the "Play" drive. Upon restart I didn't get any dual boot screen and booting (F12) to the "Play" drive resulted in a BSOD stating, "inaccessible boot device".
  6. Checking the "Play" drive in Diskpart showed that Easy Recovery Essentials has converted the "Play" drive back to MBR.
  7. ... and that where I am at!!
I feel I should just clean the whole mess up and rebuild the UEFI Boot sectors etc from scratch, but I don't know where to start now.

Reinstalling the "Work" drive would only be a last last last resort option.

Maybe the below DISKPart / EasyBCD overview helps:

https://drive.google.com/file/d/1ZUo5AagaXF65w_xYS6hRSKMeZUb27waa/view

Thanks!
 
Jan 11, 2021
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I ran the command in Command Prompt (as administrator) from my "Work" installation (correct?)

I still don't get a Dual Boot Menu, but..

On restart, it still goes straight to the Work drive without any dual boot menu. (850 EVO 500G being the Work Drive, 970 EVO 1T the Play Drive)





I can now boot to the "Play" installation through the Bootmenu (F12)



These are the Disk Management results taken from the "Work" Drive:




And these the results taken from the "Play"Drive:




Any ideas?
 
Jan 11, 2021
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I am willing to believe you Colif, but it used to work flawlessly. It strikes me that it should therefore be possible to get it working again (?)...
 
I ran the command in Command Prompt (as administrator) from my "Work" installation (correct?)
I still don't get a Dual Boot Menu, but..
Any ideas?
You updated bootloader on Disk 4 (instead of bootloader on Disk 3).

Multiple bootloaders are, what is causing confusion here.
If you want to use both bootloaders, then execute this from both windows installations. It will add second bootloader entry on both bootloaders.
bcdboot d:\windows /d

Personally - I'd just get rid of second unnecessary bootloader.
Remove boot options #2 - #8. Only one boot option in necessary.
 

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