If your modem is connected to the internet, but your computer is not getting online, you should check the network preferences on your computer:
- Go to the Apple Menu, and under Control Panel select TCP/IP.
- In the TCP/IP Control Panel, click on the Connect via: menu and selectEthernet.
- Click on the Configure: menu and select Using DHCP Server.
- Click on the File menu and select Quit.
- On the warning dialog box that asks “Save the changes to the current configuration?”, click the Save button.