You have two drives set up for dual booting, but your system only starts when both are connected.
You have two drives set up for dual booting, but your system only starts when both are connected.
I possess two copies of Windows 10, each on a separate boot drive. When both are connected, the standard Windows menu appears at startup, allowing you to select which operating system to boot from. However, if one drive is disconnected and you restart, neither will start despite having a valid installation. It either jumps straight to BIOS or displays "insert boot media." Since this is UEFI setup, the system status in BIOS indicates the drive is connected but fails to boot. The boot order lists "UEFI Hard drive" first, suggesting it should work. In short, selecting from both drives functions normally when both are powered on, but removing one prevents booting. I’m also using F11 during startup to manually pick the boot option. I notice the SSD labeled "PNY 960GB ssd" appears, and selecting it prompts for a reboot with device selection. I’m certain Windows can boot from that drive.
You have two drives, A and B, both running Windows, but each requires the other to start. It seems Windows used the other drive to store boot information during installation. To fix this, disconnect one drive, reinstall Windows on the other, then reconnect and install it back. You might also attempt a repair installation by unplugging drives one at a time, or use PowerShell/Command to generate the necessary boot files—though these approaches are more involved. Alternatively, consider using Macrium Free and selecting the "Fix Boot" option for each drive.
I'm using Macrium Rescue Media in Fix Boot mode. I notice only my first drive appears, showing two windows on each drive. It looks like it should display both drives with one installation each. Would it be better to remove the boot option from the D drive so I can boot from C alone? That way, I could reinstall without having C connected.
Create a Macrium boot disk using a 1Gb or larger flash drive. Disconnect drive D, start the process with the Macrium disk, resolve issue C. Then disconnect C, connect D back in, restart via Macrium, address issue D. This should produce two separate Windows installations that can boot independently. Both will recognize each other's drives when connected, though care is needed during setup to avoid conflicts. This approach should meet your requirements.