AirPort - Complete Power Recycle

Anytime you change networking hardware, Internet Service Providers (ISP)s, or make any significant configuration changes to your network, it is always a good idea to perform a complete power recycle of all of your networking devices.

The following should be performed as a minimum:

1. Power-down all of your network hardware devices. That includes the modem/gateway, Time Capsule, AirPort Extreme, or AirPort Express, Ethernet switches, and computer(s). Note: The power-down order does not matter.
2. Disconnect the Ethernet cable from the Internet modem/gateway from the "main" AirPort base station's WAN (circle-of-dots) port.
3. (Optional) While all of the devices are powered-down, perform a "factory default" reset on the base station(s). This will get it/them back to its/their "out-of-the-box" configuration and make setting it/them up much easier, especially if you use the "Assist me" process within the AirPort Utility. After the base station(s) reset(s), go ahead and power it back down. Ref: How to reset you AirPort base station - Apple Support
4. Reconnect the Ethernet cable from the "main" base station to the Internet modem/gateway. Verify that the cable goes between the LAN/Ethernet port on the modem/gateway to the base station's WAN port.
5. Power-up the modem/gateway; wait at least 10-15 minutes to allow it adequate time to initialize. (You may need to refer to the modem's/gateway's user guide for the details.)
6. Power-up the "main" base station; wait at least 5-10 minutes for it to completely initialize. Note: The base station's LED status light may continue to flash amber after it has initialized. That is because, there may be some additional configuration items necessary, like setting up wireless security, before the overall setup is completed to get to a solid green LED status light.
7. Power-up your computer(s).

Note: After a factory default reset, the base station will broadcast an unsecured wireless network with a Network Name (SSID) of something like: Apple Network NNNNNN. Network clients, connected to the base station either by wire or wireless, should now be able to access the Internet through the ISP's modem/gateway. Once Internet connectivity has been verified, you can use the AirPort Utility to configure the base station for wireless security and any other desired options.