I decided to make a new, clean Win10 Installation. After booting the OS Sierra Stick (for format the Win SSD), the filled line stop at approx 80%. After that, nothing happened.... I tried it with the Recovery partition, same effect. Any idea?
Update: With an Macbook Pro the Sierra Stick booted correctly. On this way, I could delete the Win SSD with the disk utility.
But, after booting the Win10 Stick ("boot from CD") I see the same blinking white dot and nothing happened. The same problem as with the former Win7 Legacy SSD.