Troubleshoot external networking devices on Mac
If you’re using an external networking device—such as a hub or a Wi-Fi router—and are having trouble connecting your Mac to the Internet, check the devices or cables for problems.
Check that all the devices are turned on and have started up completely.
Make sure all modem cables are plugged in and firmly inserted. This includes the modem’s power cord, the cable from the modem to the wall jack, and the cable from the modem to your computer. To be sure a connector is properly inserted, disconnect and reconnect it. Be sure that cables have not been cut, chewed, or otherwise damaged.
If you’re using an Ethernet hub, router, or gateway, make sure all cables and power supplies are properly connected. If you have more than one power supply available for a type of hub or router, try switching the power supplies. A defective power supply may affect network traffic.
Turn off the power on your DSL or cable modem for a few minutes, then turn it back on. Some service providers recommend that you unplug the modem’s power cord to turn off power to it (this is required if the modem does not have a power button). If the modem has a reset button, try pressing it before or after unplugging the modem and plugging it back in.
Check the indicator lights on the modem. Some DSL and cable modems have indicator lights that provide useful information about the modem’s connections. A “cable” light may indicate that the cable network is available, whereas a “PC” light may indicate that the modem recognizes the connection to your computer. If these indicator lights remain off after you have checked your cables and turned the power off and on, check the documentation that came with the modem, or contact your ISP.
If you use more than one device—such as a DSL or cable modem and a router—to connect your computer to the Internet, try turning off all the devices, waiting a few minutes, then turning them back on (turn on the device closest to the Internet connection first, let it restart completely, then turn on the next device).