The lights on the front of a cable modem detail the state of your modem's connection to the Internet. Knowing the purpose of each light can be invaluable in a troubleshooting situation. The lights can help isolate whether the problem is on the computer end, router end, or within the modem itself. It also will eliminate whether the problem originates from the Internet provider itself. The order the lights appear in may vary from manufacturer to manufacturer, but the same basic lights appear on all modems.
Find the light marked "Power." This light is lit if the modem is connected to its power source. Make sure the light is lit. If not, check the connection on the back of the modem to make sure it is secure. Check that the plug on the end of the AC adapter is securely in the wall socket.
Find the light marked "Receive." If it is on, the modem is receiving data from the network. If it is off, there is no data getting through to the modem.
Find the light marked "Send." This light is lit if the modem can send data to the network. The light should be lit. If it is not, check the Ethernet cable that runs from the modem to the router or computer for a secure connection.
Find the light marked "Online" or "Internet." This light indicates whether an Internet connection is present. If the light is on, the cable connection is functional. If the light is off, the problem is the Internet signal itself. The problem is not the service provider but in the network or modem itself. Make sure the cable is attached to the back of the modem snugly. If it is, contact your service provider to schedule a maintenance visit.
Find the light marked "PC Activity." This light will flash when the computers on the network are sending or receiving data. If the network is functioning correctly, this light should flash regularly.
Find the light marked "Standby." Standby mode is activated by pushing a button on the top or back of the modem. When in standby mode, the modem maintains its Internet connection, but all network traffic is halted. If the light is lit, the modem is in standby mode. Deactivate standby mode by locating the standby button and pressing it one time. The standby light should go off and Internet traffic should continue as normal.