New Gateway bought, only blinks yellow light

I got this Xfinity Gateway yesterday at around 5:00 EST, during an outage. Obviously I wouldn't have tried using it if I had known beforehand. I plugged it in, went through the hoops, but never actually connected it with my phone. The white light went away, after I was asked to name my WiFi.

Reset it, unplug and replugged it, waited hours, screwed in the coaxital cords, browsed this very forum all night, but I can't get the white light to come back. I don't even really know what I'm supposed to do. The app is so vague and assumes things will just work... and they haven't.  I'd hate to have to wait an entire week for a technician to come help fix this, so I'm just throwing out a desperate final plea. I'm more than happy to elaborate, if anybody has any idea what to do.