As an answer to sea, the BIOS of the version mentioned up above requires such a written line on the usb-media, though unpacked. It is an msi-board, the menu itself got some 12 entries for the boot sequence. So it may wasn't correct to put it like this, but until UEFI or something like this, I really never had to make such a fuss writing or connecting the boot media with on single bit of the BIOS. Or even a command-line for such a media. Who may is into this trouble with UEFI may knows about this. Nonetheless I am repairing my GRUB.
And yes he may looks to a former partition with an MBR, because there has been a pre-installed version of UBUNTU. As my attempt was to get unetbootin to install another OS (Debian). My problem startet. In this very case it is not the OS, whether UBUNTU or anything else, it is UEFI that stubbornly blocks any attempt to get access.
And learning from this article
https://www.linux.com/learn/tutorial...ub-2-on-linux/
I must be a fool to think there still is a MBR. This has been ages ago, nowadays it is called "shiny new Globally Unique Identifiers partition table (GPT)".