Sorry, but I will close the topic by giving the answer myself :-).
I was realy lost but tried the following (based on some other reading)

I changed the cable and took the short usb cable that I found in the box. I plugged, made myself ready with the erase process I pressed the on, pressed the reset and released, release the on The com6 was again an option on the m5 burner. I started by erasing, the clic clic was still present. I burned a new firmware, the machine is working again.
I hope it will help similar cases :-)