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#11
Since the computer is an AIO, I found this for a Dell AIO Inspiron 20-3052. The system board is very difficult to make out, but does it resemble what your system board looks like?
You could go on another computer, plug in the Dell service tag number and should be able to access the manual for target computer and look for specific information. If the version isn't 3052 please let us know.
--- You could also go to Dell on-line support and ask them if there are password reset jumpers on that system: naturally you'll want to explain why.
Since you mention the media creation tool, it appears to me you created install media via a USB or DVD.
It might be possible to disable Fast Boot.
--- Use the USB or DVD install media to see if you can get to Command Prompt: hopefully it will allow you to use it as (Admin).
--- If you can, enter powercfg.exe /hibernate off. If it takes I believe it turns off Fast Boot.
--- I've read re-starting a computer circumvents Fast Boot but if you actually can set Fast Boot to stay off it's better.
On having changed secure boot and the inability to return to legacy boot (those may be backwards): that's a tough one. However if you can do a System Restore via your install media, maybe that will help: I know that since the BIOS is involved, it might not work but I would consider it based on what else was changed on the computer maybe even in the registry.