xps 12 boot from usb

I have a XPS 12 9Q23 which had gotten very slow, and I would like to reinstall windows.

I downloaded and used the 'windows media creation tool' from microsoft, which would handle the process, which includes a few reboots. During one of those, however, the boot process didn't move past the dell logo.

Researching this a bit, I tried the guide under [1] (below), as the symptoms pointed to a no-power-on-self-test situation. This did not solve the problem.

The I did a diagnostics test, which the laptop passed without problems; also the thorough tests were fine.

My thought then was to reinstall windows using a bootable USB drive. I got an ISO from here [2] and created such a drive using several methods found online, from both a windows machine and an ubuntu linux machine.

Now the problem seems to be, that the USB drive is not found or recognised by the laptop while booting. I tried several things, including secureboot enabled/disabled and EFI enabled/disabled. The USB drive is never showing up.

I'm at the end of my ideas. Does anyone know how to solve this problem? Many thanks.

[1] http://www.dell.com/support/article/de/de/debsdt1/SLN127732/en

[2] https://www.microsoft.com/de-de/software-download/windows10ISO