I have a Nortel ICS 6.1 system With three VOIP lines provided by comcast. Last Friday 2 of the lines went dead. I can select them on the T-7316e but there is no dial tone on line 1 or line 2. Line 3 works fine. I checked the Comcast modem and there is dial tone coming out from the modem to the 66 block. Not sure where to go from here. Any suggestions would be appreciated.