BOOTMGR is missing error: How do I fix this?

Hey,
I’ve been digging through Google, but I’m still hitting a wall here.
Basically, I have this machine that was running on 2GB of RAM, but I just added another two gigs, so I'm sitting at 4GB now. It’s currently running 32-bit Windows 7, but my goal is to move up to Windows 10 64-bit. I already double-checked, and the processor definitely supports 64-bit.
My teacher at school helped me out by putting the Windows 10 64-bit installer onto a USB Hard Drive. I plug it into the computer, fire it up, and I've set the BIOS to boot from the USB Hard Drive, but then I hit a snag. The screen just says "BOOTMGR is missing
Press Ctrl + Alt + Del to restart"

Has anyone run into this before? Any idea what I'm doing wrong?
Thanks, everyone.

I think you might have actually made a "proper" bootable USB stick. Maybe try booting from it on a different computer—just to see if the exact same issue pops up there?

If you were just copying the Windows ISO file directly onto the USB drive, you should probably use Rufus instead.

Absolute legend!
I've been wrestling with this mess for a few days now, messing around with some partitions over here, all because I need to grab one specific program lol.
Thanks a ton, man! 😁

Exactly—if you’ve got the Windows ISO ready to go, just burn it using Rufus. Just make sure you hit those specific settings in Rufus: create a bootable disk using ISO image