Windows 10: Can't boot into main drive after installing Windows on another drive

When you installed Windows onto the M.2 SSD, you still had the SATA SSD installed. Windows setup found the EFI System Partition on the SATA SSD and put the boot files there instead of the M.2 SSD. That is why we recommend that you have only the drive connected that you want to install Windows on until the computer is successfully booting from it, then connect your other drives.

Now, if you don't want to do a reinstall that way, you will have to make room on the M.2 SSD for an EFI System Partition formatted as FAT32 (250 - 500 MB in size) and manually create the boot files on it.

Starting with a screenshot of disk management will help:
Disk Management - How to Post a Screenshot of Windows 10 General Tips Tutorials

NavyLCDR said:

When you installed Windows onto the M.2 SSD, you still had the SATA SSD installed. Windows setup found the EFI System Partition on the SATA SSD and put the boot files there instead of the M.2 SSD. That is why we recommend that you have only the drive connected that you want to install Windows on until the computer is successfully booting from it, then connect your other drives.

Now, if you don't want to do a reinstall that way, you will have to make room on the M.2 SSD for an EFI System Partition formatted as FAT32 (250 - 500 MB in size) and manually create the boot files on it.

Starting with a screenshot of disk management will help:
Disk Management - How to Post a Screenshot of Windows 10 General Tips Tutorials

Thanks for letting me know! I didn't know it would do that. In the future I'll disconnect all other bootable drives except for the one I'm installing on. Now, would you recommend me reinstalling Windows or manually creating the EFI System Partition and boot files? If I manually create them will they be the same exact thing as the ones reinstalling Windows would create, and could I potentially run into any problems later with the manually created ones that I wouldn't if I just reinstall Windows?

I'll be back home in a few hours, will post a screenshot then. Thanks again!

TechnoMage said:

Just to avoid collisions between several OS's, (I have six drives in my main PC, that could possibly boot the system)
I make sure my main drive is connected to SATA port "0", on the motherboard, and that all other drives are either unplugged from the SATA ports or not powered up.

Right now, I'm running on a hard drive sitting on the desk next to my tower, on which I've just installed Windows 10, Pro, 64.
My main drive, a 128 SSD, mounted inside my tower, is unplugged. I like to keep peace in the family! lol

Cheers Mate, and Good Luck,
TechnoMage

Thanks for the tip TechnoMage! I'd definitely like to do that, problem is my M.2 SSD is underneath a cover that gets screwed into my motherboard, which is underneath my graphics card. It isn't very convenient to get to anytime I want to boot to my SATA SSD. To stop them from reading/writing to one another when I've booted into one, would simply removing the drive letter of the other bootable drive work?


And here is my Disk Management window:



C: in this case is my SATA SSD. E: is my M.2 SSD with my main Windows installation and D: is a data HDD. Looks like my M.2 SSD is missing an EFI partition afterall. What should I do?

Thanks!

Just build an EFI System Partition on on the m.2 SSD. I'll post instructions when I get out of the hot tub :-).

Here's my disk layout, I will be adding an EFI System Partition to my Disk 0. You will have to adjust a few of the commands to match your drive # and drive letter of the Windows you want to boot.



I ran these commands in a Command Prompt (Admin). I believe they will also work in a PowerShell (Admin):

Code:

Microsoft Windows [Version 10.0.10586]
(c) 2015 Microsoft Corporation. All rights reserved.

x:\windows\system32>diskpart

Microsoft DiskPart version 10.0.10586

Copyright (C) 1999-2013 Microsoft Corporation.
On computer: MININT-KDT67KV

DISKPART> list disk

  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk 0    Online          447 GB  7168 KB        *
  Disk 1    Online          931 GB  1024 KB        *
  Disk 2    No Media           0 B      0 B

DISKPART> select disk 0

Disk 0 is now the selected disk.

DISKPART> list part

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    Reserved            16 MB  1024 KB
  Partition 2    Primary            447 GB    23 MB

DISKPART> select part 2

Partition 2 is now the selected partition.

DISKPART> shrink desired=100

DiskPart successfully shrunk the volume by:  100 MB

DISKPART> create partition EFI

DiskPart succeeded in creating the specified partition.

DISKPART> format fs=fat32 quick

  100 percent completed

DiskPart successfully formatted the volume.

DISKPART> assign letter=z

DiskPart successfully assigned the drive letter or mount point.

DISKPART> exit

Leaving DiskPart...

x:\windows\system32>bcdboot C:\Windows /s z: /f UEFI
Boot files successfully created.

x:\windows\system32> exit

Notes about some of the commands:
Select Disk # <- Select the disk # of the disk you want to make bootable.
Select Part # <- Select the partition # of the Windows partition that is occupying all the space on the drive
bcdboot C:\Windows /s z: /f UEFI <- Change the C: to the current drive letter assigned to the Windows that you want to boot.

After the commands are completed, you will probably need to enter you UEFI setup when restart your computer to set it to boot from the new Windows Boot Manager on the drive you want to boot from. After you are boot from the desired drive, if the new EFI System Partition has a drive letter assigned to it, you can (and should) remove that drive letter from it in disk management.