It sounds as though it has not been provisioned to RIngCentral's servers. Did you purchase the phone directly from RingCentral? If you did, it should have come pre-provisioned. If not, you will have to call RingCentral support to have them provision it for you.
This may seem like a silly question, and it's not meant to be sarcastic, but you don't mention whether this happened or not... Did you plug an Ethernet cable into it AND into the correct port? No internet = a dead phone. If (good) internet is supplied, then J.B. Ferguson's thought would come into play next.