Okay, problem solved. I get now an address with DHCP and my cablemodem ISP.
I think there were two problems, one was a problem of my ISP, I assume DHCP didn't work well for a few days. My other machines got the same IP address for days (which isn't normal with my ISP).
The other problem was, that the Miami config file I had (was burnt on CD), had a wrong MAC address in it.
I don't know which one, but not mine for sure. I changed it manually to my own MAC address and oups, it worked and I'm happy now and installing YAM.
But by the way, during troubleshooting I found some strange things:
I tried Genesis but when I started it I got the message:
genesis needs chooser gadget v44 installed is 41.110 (Morphos and my classic Amiga WB 3.9 both have 41.110 installed).
The installer is not able to create Directories. Okay I now know it's the default icon problem I will fix that later.