Recently my father-in-law, who lives in Lexington, switched to Insight cable for his internet connectivity. He's been using an old Dell PC, with no problem obtaining an internet connection.
Today, we surprised him with an new iMac. The iMac would pull an IP from the cable modem. Spoke with Insight who said there was no special DHCP/network configuration required. Spoke with Apple, who had me try many things before finally reinstalling the operating system from scratch. Still, the iMac would not connect to internet. (Could only get a self-assigned IP.)
Brought iMac home to Louisville, thinking the ethernet card in the iMac would need to be replaced. Plugged it into my own Insight cable modem (same model as my fa-in-law's) and, whaddya know, the iMac got an IP address and connected to the internet just fine.
Cable modem is new Motorola Surfboard SB5120. Longest time we kept it unplugged was five minutes.
The Dell, again, has no problem obtaining an IP address.
My instinct is to try to things: (1) try the Lexington connection with my cable modem. (2) if that doesn't work, then to move the iMac to another room and try a different cable connection. (e.g., unplug a TV).
Appreciate any responses.