[melevittfl]

OK,

On the cable modem, there should be a light labeled "Enet". When you plug the ethernet cable into the iMac, that light should light up.

If it doesn't then your iMac and your cable modem aren't making a physical connection. Before buying a router, try a new ethernet cable.

If the light does come on, that your iMac is making a physical connection, then, can you please open the Applications folder, then open the Utilities folder and run the Terminal application. You'll see a black screen with a command-line prompt. Type "ifconfig" (without the quotes) and press enter. If you could, please copy and paste the output so we can see it.

Thanks,
Mark