|How are you connecting to your highspeed? |
Is it going directly from the modem into the laptop? If yes contact your ISP as they may have it set to only accept one MAC address. Since you've changed units, your MAC will have changed as well.
You might want to consider a SOHO router. With one of those, you not only get a firewall and DHCP, but you could also connect up to 4 PCs/laptops if you get one with 4 LAN ports.