Virtualbox Error: "No Bootable Media" while using .iso

I saw another thread from a few years back, but the solution seemed to be "Make sure you're booting from the right device."

When I first set up the VM, then start it, it asks for a file or location to boot from, which I then give it the desired .iso file. In this case, Windows XP, a fresh ISO directly from the Microsoft website, and I've even tried a few from other sources, too. No matter what I do, booting from the ISO directly, it doesn't work, and I've even tried burning the ISO to a USB, and trying it on my secondary "testing" computer. Both it, and Virtualbox, report "No bootable media. System halted."

I am booting from the correct source, so that's not the problem. I also do not have the ability to burn a CD, as I do not have a disk drive, disks, or ability to attain either. I'm limited to a USB drive, and .iso files.

What are my options here?


Or, if there is a way to dual-boot Linux and Windows, easily, I'd be willing to give that a go, too. Should I make a second thread for that?

Is there something simple that I'm not seeing here in Virtualbox? It's exactly the same process I've used for years, but suddenly, it doesn't want to work.