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After a power outage, a friend's iMac powered up but the AirPort is flashing yellow and the computer cannot get on-line. What is the "power up order" to properly connect?

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doesn't matter, it's apple. Make sure you power down and power up your internet modem. –  obeyObama Mar 21 '11 at 3:26
    
thank you. yes all devices have been powered down and up waiting 3-5 minutes between times. Why is the light flashing yellow? please. thank you –  Adie Mar 21 '11 at 3:31

2 Answers 2

"Startup is complete, but AirPort Express didn't get an IP connection.", from here. If my experience with Time Capsule is any guide, this can mean your modem or modem/router is down or its DHCP service hasn't come up, or, if it's pure modem (no router) perhaps your ISP's DHCP isn't restored.

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First, figure out of the problem is between the iMac and the base station, or between the base station and the DSL modem, or between the DSL modem and your DSL ISP.

  1. Check if the iMac's AirPort Menu Extra (the AirPort signal strength bars in the menubar) shows signal strength.
  2. In System Preferences > Networking, see if the iMac has a valid IP address (it'll probably be something like 10.0.1.2).
  3. Launch the AirPort Utility (/Applications/Utilities/AirPort Utility.app) and see if it can see the base station.
  4. From the AirPort Utility, open the base station's configuration by double-clicking it in the list of available base stations. Click on the "yellow light" button to see what problems the base station is reporting -- any time the base station is flashing yellow, you can use the AirPort Utility like this to see what it's problem is. Resolve (or choose to ignore, if you know what you're doing) each of the problems it's reporting.
  5. Go to the Internet tab of the base station's configuration and see what it reports for its default gateway. From the iMac, try pinging that gateway (you can use Terminal for this if you're comfortable with that, or the Network Utility in /Applications/Utilities/Network Utility.app).
  6. If the base station doesn't have an IP address on its WAN port, check to make sure the Ethernet cable is connected between it and the DSL modem. Make sure both the AirPort base station and the DSL modem show a link light for Ethernet.
  7. If all this has worked so far, you might have a DNS problem. See what DNS server addresses your base station is set to use. See what DNS server IP addresses your iMac is set to use. Use the Network Utility (or the host, dig, or dns-sd -Q commands in the Terminal) to see if you can successfully resolve host name. That is, look up the IP address for, say, "google.com", and make sure you get back an IP address.
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