I discovered a bug in BIOS.
During start up press ESC -> F10 to go to Computer setup (BIOS settings).
In the BIOS go to STORAGE -> BOOT ORDER
In the "Please select boot device:" menu, you have the following list or similair:
- EFI Boot sources
- Legacy Boot sources
- ATAPI CD/DVD Drive
- Hard Drive
Scroll down the list (by using down arrow key). When you are on the last item on the list, scroll down one more time. Then you will see that there is one more entry in the list, which is not being showed. I do not know what exactly this item is, but it let me boot from the USB stick.
Press F5 to Enable this item. Press F10 to accept then change in the menu.
Then go to FILE -> Save changes and exit.
The system will now reboot.
During start up hit ESC again and press F9 in the Startup menu.
This takes you to the boot menu and your USB will now be shown in the list and you can install the image.
I noticed that the hidden item which you enable in the BIOS resets by itself.
For me it reset after I had installed the image and taken out the USB stick.
When trying to reinstall the image once more, I had to re-enable the hidden item in the BIOS, because the memory stick did not show up.