You're post is quite confusing but we may be able to help. You say you are trying to remove the hard drive, but you don't say WHICH drive by letter designation. Which drive and letter are you having the problem with? C:, E:, J:, K:, I:?
Also, when asking a question like this it's customary to at least provide us with some basics. What version of Windows are you running? What Make/Model is the computer? Is it a desktop PC or a laptop? Is it an OEM PC (Dell, HP, Acer, Toshiba)? Self-built PC or Custom-built PC?
It's hard to solve a problem you've had for weeks or months without this kind of information.
If you didn't know which drive is the Bootdrive (C: drive), then who added all these extra drives to your computer? Did you buy it with all these drives from someone?
There a number of repair tools you can use to fix this problem, but if you remove the C: drive and it doesn't boot from the other drives, this is normal as only ONE DRIVE, THE C: BOOTDRIVE is responsible for booting Windows (commonly referred to as Drive #0). If any of your other drives are USB drives, which it appears to be, none of those drives are capable of booting Windows, so of course removing the C: drive will cause your system not to boot.
>>>@neemo: Well this would be a problem if the OP removed his C: drive (Drive #0). A system partition alone on a secondary drive won't have Windows OS anywhere. That's why I asked him the question which drive he physically removed from the machine.<<< >>>BBJ<<<
Technically speaking is boot drive is really C and I at this point since he has the two required parts spread out.
The bootmgr entry needs to point to have the "partition" entry point to the physical disk and volume. So it has to be setup like so if for example its the third volume on the first disk partition=\Device\Harddisk\Volume3 or whichever physical disk it's C is on.
You can open an Administrative command prompt and type the command below to place boot files in the C partition. Make sure and put spaces where indicated or copy and paste the commands.
bcdboot c:\windows /s c:
Then shut your system down and disconnect the other drive. During reboot, make sure drive 0 is set as the primary boot device. The system should now boot normally but you may not have recovery options available. So before you shut the system down you might run the command below in case you need the info, it should show the path to the recovery tools so save the listing.
I have practical the same issue in Win10. I used the BCDboot command the files were written (it showed) but actually nothing changed. What should I do? I need to remove my old Win7 drive (that is working at the moment) to change it inside the warranty as it has been getting bad time after time (SSD). Any thoughts?
What about the easybcd tool? How can I find it fro free?
If Windows is on Drive C:\ you should be able to tell EasyBCD to create a boot sector on Drive C:\, after that it should boot from drive C:\ .
EasyBCD will be able to see what drive Windows is on if you ask it scan for operating systems.
After you have changed it in EasyBCD reboot the computer and bring up the boot menu, f8 on my computer, and tell it to boot from Drive C:\.
Make sure that it shows C:\ as an available bootable drive and then boot to it.
Then unplug the other drive and try rebooting once more you should be good to go.
You can do the same thing manually as Saltgrass described.
All you can do is try, the other option is to reinstall Windows on the drive you want to boot to, with the other drive unplugged so that it will create the boot sector and install the OS all at the same time on the new drive.
I've always had good luck with EasyBCD, and it's easy (as it says), to use but I haven't done what you are trying to do in a long time so it's not fresh in my mind. But if I remember correctly you only have to select, Change boot drive, Select the drive you want to boot to, and click go ahead or something like that, and it will do it automatically.
Read though this and see if it's what you are looking for.