The Roon support queue is quite long and may take a week or two.
I assume you have tried rebooting your Nucleus and router. You might try connecting your Nucleus to a monitor or tv with HDMI input and a keyboard and post what you see on the screen.
I connected a screen and all I get is no signal…while the network green ligh blinks and the power button illuminates…from what I’ve read this sounds like the ssd @noris some support soon???
If there is no HDMI output, we are likely dealing with a motherboard issue. I’ll follow up via private message to get your purchase details, we’ll likely have to start an RMA for this unit.