Boot to external harddrive (has bootable windows 10 image on it) via USB

The Facts:
I have a 1 TB USB external hard drive that has a CUSTOM Windows 10 image on it that's bootable. The image is 30 GB so it could not fit on a Blu Ray. I have a standalone (not connected to the internet) Dell 9020 mini PC (with wiped hard drive) that I would like to install my bootable CUSTOM Windows 10 image on from the external hard drive.

The Problem:
I've had no success in getting the Dell 9020 mini PC to recognize my external hard drive as bootable media (F2 or F12 on boot). I've tried the following google results to no avail:

Any other suggestions? Thanks in advance
Who is Participating?
McKnifeConnect With a Mentor Commented:
About blueray as an option: there are different types of bluerays, I have some here that hold 100GBs.
Wikipedia says:
25 GB (single-layer)
50 GB (dual-layer)
100/128 GB (BDXL)
Cliff GaliherCommented:
Putting a bootable image on a hard drive does nit make the hard drive itself bootable. And just as importantly, windows uses a separate bot image to install an install image. It is a two-step process, and you've tried to mash it together. That'll never work.

You need to create a boot image with a setup program to lay down your custom install image. And be sure you are properly licensed to do so. Entire books exist on the subject, so its worth grabbing one if you are new to the process as it appears.
Is the bootable image an iso file? If so, use WinSetupFromUSB to create a bootable USB stick or disk from the iso file. Make sure you use FAT32 as the format of the stick or disk, not NTFS, as otherwise you won't be able to install to a GPT disk and UEFI BIOS. As is well known, FAT32 doesn't support files larger than 4GB, but the tool that creates the stick splits the iso file into 4GB sections so it will still work.

One thing you'll also have to make sure, is that you connect the stick/disk to a USB 2 port on your destination PC, and not a USB 3 port. If you want to use a USB 3 port, you'd have to integrate the USB 3 port's drivers into the boot.wim file as far as I know.

I don't know your Dell's BIOS, but often USB connected disks or sticks show up under the HD disk selection, so often you have to select which disk has boot priority in the disk selection.
how did you put the image on the external drive?  with what software - and /or - procedures ?
jslaughtAuthor Commented:
The best easiest solution for my situation.
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