How can I boot Windows at external hard drive from internal hard drive?

In my internal hard drive, there is a copy of Windows installed at 'sda1'. I use grub to boot into it.

In my external hard drive (internal hard drive with a box), I have a complete Windows installed normally while the hard drive was in the computer.

Now, I want to use "Windows Boot Manager" to boot the external hard drive.

How can I find the Windows in the external hard drive?

Answer

If the external drive is in a USB enclosure, then there is no way to boot Windows 7 from it. Windows does not support booting from a USB drive even if the BIOS does. It's not a GRUB or boot loader thing. Windows 7 just doesn't support running from USB period.