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  1. #1
    Senior Member
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    Default "Operating system not found" after changing active HDD

    Win10 is installed on SSD and documents on a secondary 1tb HDD. I wanted to upgrade to a 2tb so copied all my data from the 1tb then replaced it. Win wouldn't boot without it plugged in, so booted up again and checked the status in computer management. I noticed the 1tb was set as active instead of the SSD so I set the SSD to active, rebooted then got the error "Operating system not found" on boot, with or without the 1tb plugged in. Every step of the way the SSD was always first to boot in BIOS. Win10 is installed on the SSD so I don't know why it says there's no OS, I only used the 1tb for documents.

    Win10 1809
    disk management: https://imgur.com/a/HpxCZxB
    Last edited by Vicx; 03-10-2019 at 10:54 AM.

  2. #2
    Computer Technician wainuitech's Avatar
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    Default Re: "Operating system not found" after changing active HDD

    The cause will be because the boot loader is on the 1TB drive not the SSD, if you had of cloned the 1TB it usually brings the boot loader with it.

    By changing the active from the 1TB , it basically broke /removed it.

    You can try rebuilding the boot loader ( leave the other drives disconnected) by the method in this video on youtube https://www.youtube.com/watch?v=55NnSkuv3rM Sometimes works sometimes Not.

    Had similar yesterday and used Macrium reflect to fix it, you need to download, install on a working computer, then make a ISO CD / USB and boot from that, follow instructions https://kb.macrium.com/KnowledgebaseArticle50168.aspx

    Again sometimes works sometimes not.
    Update / Upgrades = Replace old bugs with new ones.

  3. #3
    amateur expert dugimodo's Avatar
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    Default Re: "Operating system not found" after changing active HDD

    This is why it's recommended to install windows with only a single drive connected because windows installer likes to put boot files on other drives if it finds them. MS either need to stop this practice or make it an obvious choice during setup IMHO.

    Hopefully Wainuis link helps, I've had success sorting this in the past using EasyBCD to repair the bootloader but to do that you first need to boot into windows. For me on discovering the PC wouldn't boot I put the old second drive back in, loaded up EasyBCD and used it to make the C: drive bootable, then removed the drive again and booted up.. There are probably better methods but this one was easy and worked for me.
    Ryzen 2700X, 16Gb DDR4RAM, 512GB M.2 NVME SSD, MSI GTX1070

  4. #4
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    Default Re: "Operating system not found" after changing active HDD

    I see that you have Win10 1809 on the SSD. What you could try is leave the 1TB attached, go to Microsoft media creator, download the ISO for 1903 and then burn that to a DVD (your system is probably 64bit). Turn the PC off, disconnect the 1TB leaving just the SSD and the optical drives attached. Install the 1903 from the DVD to the SSD.

    Reboot and see that it works. Turn the PC off, attach your HDDs and you should be able to reboot to the 1903 operating system.

  5. #5
    Senior Member
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    Default Re: "Operating system not found" after changing active HDD

    Quote Originally Posted by wainuitech View Post
    Had similar yesterday and used Macrium reflect to fix it, you need to download, install on a working computer, then make a ISO CD / USB and boot from that, follow instructions https://kb.macrium.com/KnowledgebaseArticle50168.aspx
    I spent ages trying to make a bootable Win10 USB, had vague errors every step of the way, even once I finally got into it. Gave up and tried Macrium and it was done in minutes, didn't need to read a tutorial, it was all straight forward. Everything's working fine now.

    Quote Originally Posted by dugimodo View Post
    This is why it's recommended to install windows with only a single drive connected because windows installer likes to put boot files on other drives if it finds them.
    I've learned my lesson now, will make sure only the SSD is plugged in during installation next time.


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  6. #6
    Senior Member piroska's Avatar
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    Default Re: "Operating system not found" after changing active HDD

    Quote Originally Posted by wainuitech View Post
    The cause will be because the boot loader is on the 1TB drive not the SSD, if you had of cloned the 1TB it usually brings the boot loader with it.

    By changing the active from the 1TB , it basically broke /removed it.

    You can try rebuilding the boot loader ( leave the other drives disconnected) by the method in this video on youtube https://www.youtube.com/watch?v=55NnSkuv3rM .
    There are other programs too, I've always managed to fix it.
    As he says....you broke the boot loader.
    Ex-pctek

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