RBR50 Switched from Comcast Modem to Infinity Modem

Switched my RBR50 from a Comcast Modem to an Infinity residential Modem including chaning over the internet provider. The Router is now Magenta and cannot be logged into even via ethernet cable. Did the usual turn on and off, pluy and unplug etc etc. Likely needs a firmware update, but cannot get it online. Likely and easy fix but no luck. Thanks.