What to Check
The first things to check if you cannot access the Internet are:
1. The modem is powered on.
2. The hardware connections are established.
3. The lights on the modem are on. (Power, Ethernet, DSL)
Check the Wiring
1. Ensure that the cables between your modem, your computers and your telephone jacks are connected firmly. Loose connections can affect your Internet connection.
2. Damaged cables can interfere with your Internet connection. Check for damage along the cables and loose connections at the end of the cable. Replace any damaged cables.
3. Ensure the phone cable that runs from the modem to the wall does not go through a filter, splitter, surge protector, or extension cable.
Test the Telephone Cord
To eliminate the possibility of a fault with the telephone cord itself, try the following:
1. Use that telephone cable in a telephone and make sure you can hear a clear dial-tone with no noise.
2. Try swapping out that telephone cable with one from a phone known to carry a clear signal.
Power-cycle your modem
Loss of Internet or network connectivity can be caused by the computer. Often a reboot will rectify the problem. To perform a complete power-cycle, following the instructions here.