Move Cable Modem to Another Room

Hello,

I'm trying to move my cable modem from my living room to my office which should be straight forward. Apparently not. I've connected the coaxial to the coaxial drop in the new room, powered on the modem, and it just sits there blinking green. No amount of waiting changes this and I ultimately moved all of it back to my living room, connected it back up, and within a minute the connection was established. I'm not the original home owner or whoever installed the cable so I don't have a clue where there might be a splitter or which connection is the right one. I did see a gray box on the north side of my home but it has a number of coaxial cables going into it so it's probably any of those? How can I get this moved? I tried going to Xfinity Assistant to schedule a technician but it finds no problem with my connection since it's obviously connected to the living room. No problem meant it didn't let me schedule anything. Any assistance would be wonderful.