Was a bit too quick here, found the solution for this. Using the power-button BIOS upgrade procedure brought the USB connection back to life.
- Press and hold the power button down for 3 seconds. Release it before the 4 second shutdown override.
On the other hand, has anyone managed to get the stick booting headless in "Ubuntu mode" ? It seems that it gets stuck somewhere, but i cannot determine where in the boot process. And if I reconnect the display after power-on, there is NO picture at all... And the operating-system does not boot, in example there is no connectivity through the USB-to-ethernet adapter.
I have only tried Ubuntu 15.04 with numerous different grub options, since the 14.04 Installer does'nt seem to recognize the mmcblk storage device out of the box.