Apple iMac (21.5 and 27-inch, Late 2009) - Manual (Page 51)

Chapter 4 Problem, Meet Solution 51
Cable Modem, DSL Modem, and LAN Internet Connections
Make sure all modem cables are firmly plugged in, including the modem power cord,
the cable from the modem to the computer, and the cable from the modem to the
wall jack. Also check the cables and power supplies to any Ethernet hubs or routers.
Turn the modem off and on and reset the modem hardware
Turn off your DSL or cable modem for a few minutes, and then turn it back on. Some
ISPs recommend that you unplug the modem’s power cord. If your modem has a reset
button, you can press it either before or after you turn the power off and on.
Important: Instructions that refer to modems do not apply to LAN users. LAN users
might have hubs, switches, routers, or connection pods that cable and DSL modem
users do not have. LAN users should contact their network administrator rather than
an ISP.
PPPoE Connections
If you are unable to connect to your ISP using PPPoE (Point to Point Protocol over
Ethernet), make sure you have entered the correct information in Network preferences.
To enter PPPoE settings:
1 Choose Apple () > System Preferences.
2 Click Network.
3 Click Add (+) at the bottom of the network connection services list, and choose PPPoE
from the Interface pop-up menu.
4 Choose an interface for the PPPoE service from the Ethernet pop-up menu.
Choose Ethernet if you are connecting to a wired network, or AirPort if you are
connecting to a wireless network.