Hi cynerd
My Cisco switch says there is no link and the port ist down. 
I’ve tried to setup a static IP on my notebook and plugged in the ethernet-cable directly to the router, yes. But I was not even able to ping! My notebook as well says the ethernet-cable is not connected (red status in network-settings). I’m not sure if it is a hardware-related issue. What does these blue LED mean?
I’ll check the DHCP issue as well, but can’t imaging this is the problem in this case.
Right now, after resetting and restoring the settings, the router is working again.