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A friend of mine asked me to install Windows on his new SSD. I use a dual boot system, with Ubuntu and Windows 10. I made a bootable flash USB of W10 so I could install it on his SSD, connected to my PC. I did it and everything was fine. When booting into my Windows boot manager from GRUB I was able to choose which volume I wanted to boot into; his SDD or mine. I tested them and both worked perfectly.

However, after installing his SSD into his PC, I could not boot into it. I was able to find it in the device list on his mobo BIOS, along with his HDD also containing Windows that I did not format before I made sure his SSD was working properly, but couldn't boot to it. It wasn't recognized as a boot loader, manager or anything. However, when booting into his HDD, I could acess his SSD and it contained all of the usual windows files. Any clue on what might be happening and why?

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  • What comes to my mind first is that you want to make sure you SSD partition table (MBR vs. GPT), and both your computers' boot option (Legacy vs. UEFI) should be consistent. Please confirm.
    – charlesz
    Commented May 1, 2023 at 18:29
  • You should have disconnected your drive(s) before installing his Windows. The installer used your ESP (EFI System Partition) to install the bootloader, as usual and as expected. That was dumb move because you don't want to keep that Windows bootloader, only yours. The answer is maybe useful but you'll soon find out you have no space left to do that. Better to install it properly this time around, after you understand what UEFI mode, its requirements and partitions.
    – ChanganAuto
    Commented May 1, 2023 at 18:37
  • @ChanganAuto thats does seem like the problem. Quite an oversight from me. Thanks.
    – Antônio Gabriel Zeni Landim
    Commented May 1, 2023 at 19:42

1 Answer 1

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You have perhaps not installed the boot code into the disk, as you were using GRUB on your computer.

You may add the boot code to his disk by doing Run a Startup Repair in Windows 10.

You will need to boot from the USB boot media of Windows. Ensure that his old boot disk is not connected when doing that, as the boot code could be installed on the wrong disk.

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  • It has nothing to do with GRUB. The installer selected the preexisting ESP, as usual and as expected. It would have happened the same with Windows only. What you suggest here may work but the user must shrink some partition and eventually move it in order to crete space for the ESP. My suggestion above was to reinstall it properly instead of trying to recover this one.
    – ChanganAuto
    Commented May 1, 2023 at 18:59
  • @ChanganAuto: The Startup Repair should normally shrink the Windows partition automatically. If the Windows installer on his computer would have installed the startup code, this would have replaced his GRUB or would at least has added a boot entry in his EFI partition. I don't know if he checked that.
    – harrymc
    Commented May 1, 2023 at 19:17
  • Let's hope it does. But no, it wouldn't have replaced Grub, bootloaders can and do co-exist. It wouldn't have added an additional entry either because the Windows bootloader manager can manage multi-boot scenarios. The Windows installer doesn't add a new entry when it detects Windows already installed. Ubuntu/GRUB are irrelevant and immaterial in this scenario.
    – ChanganAuto
    Commented May 1, 2023 at 19:30
  • @ChanganAuto: I have counseled several posters here that installed Windows after Linux and lost GRUB, on how to return their GRUB with dual-boot. Windows doesn't always play nice with GRUB.
    – harrymc
    Commented May 1, 2023 at 19:33
  • Booting with Grub and selecting Windows (only one option) chainloads the Windows EFI that then allows selecting from one or more Windows installations. GRUB does not and cannot select different Windows versions, even if many users wish that to be true, it's always mediated by one single Windows point of entry.
    – ChanganAuto
    Commented May 1, 2023 at 19:33

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