finished installing 10.3 to USB; will boot once when installer triggers restart; will not boot if computer is cold booted

[Alan Tu <8libra@gmail.com>]

Hi, I don't know how to fix this. I used an ISO image burned to one
USB to install Debian to a second USB. I did this twice, with just one
difference:

1) At the end of the install, both USB are connected to the computer.
When the text installer prompts me, I remove the installation USB,
then press Enter. The new Debian system boots.
2) At the end of the install, both USB are connected to the computer.
When the text installer prompts me, I remove the installation USB,
then press Enter. But this time while the BIOS is posting, I remove
the second USB and let my computer boot into Windows. I then
completely power off the machine. I then re-attach the second USB with
the installation. Computer boots to Windows. The second USB doesn't
boot.

I should add I am blind and cannot see the messages that a potential
bootloader might output.

I ran this contrived test because the bootable USB drives I installed
on only booted once. (While trying these scenarios, I'm getting quite
familiar with all the numeric menu choices in the text installer.)

When the installer boots, it is attached to /dev/sdc. (I have two
built-in hard drives.) During the install, the target USB drive is at
/dev/sdd. But when I'm booting the system with only the installation
target USB attached, that probably is not /dev/sdd at that point. It
would probably be /dev/sdc, if the kernel knows about such things at
this point. I'm not sure if this is my problem.

I have read about Grub refering to hard disks by number, like hd0. But
I just don't know what to do.

I don't want to modify my original Windows boot drive with a
bootloader. All I want is to boot into Debian when I insert the USB.
But I'm really stumped.

Alan