New CM500 modem, Online Green Light will not come on at all

Turns out the cable had been disconnected inside of the junction box outside of my townhome.  All of the neighbors' cables were okay; mine was the only one that was messed up.  A technician from Xfinity diagnosed the problem.  I have no idea when or why or by who the cable was disconnected, but the technician pointed out that the cable junction box has no lock on it.  I am pondering how to remedy that vulnerability!  Anyway, I am now up and running.  Yippie!