I had TWX come and replace a cable modem/router that was sporadically dropping off connection. They came and dropped an Arris cable modem/router/phone modem in its place. It works just fine but my computers no longer see each other on the local network. NO idea why. No settings on any of my macs have changed. I've turned off the firewall on the modem, combed through the instruction manual...i dont think i have to add MAC address or anything to get computers to see/talk to each other if they are on the same network? Any idea what can cause this?