When I plug my cable modem directly into my laptop, neither reads as connected. It's not the cable; I've tried several.

The modem was replaced last week, and works via wireless router, so that's not it either. Device mgr says the network adapter's working properly, the drivers are up to date, no new hardware / software...

System Specs
O/S Windows 7, post format:C
Broadcom 440x 10/100 integrated controller
Dell Inspiron E1505

How do I find the glitch, and how do I fix it?