"None of your preferred networks are available"
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It might help to reset the connection settings on your Mac using these steps one at a time until the problem is resolved, recognizing that, depending on your problem, not all of these steps will make sense:
1) Use the AirPort menu bar item to turn AirPort off, then on again.
2) Try to select your Wi-Fi network from the AirPort menu.
3) In the Network panel of System Preferences delete the AirPort item from the left column, then add it back.
4) In the same panel as (3), define a new location and see if you can make that work.
5) In the same panel, select the AirPort connection item, click the "Advanced" button, select the "TCP/IP" tab, then click "Renew DHCP Lease".
6) In the folder /Library/Preferences ( not <yourhomefolder>/Library/Preferences), move the folder SystemConfiguration onto the Desktop, then restart your computer. See if you can now make your AirPort connection work.
These steps may not help, but they'll only take a couple of minutes to try. Before you try these, if you have any special network settings on your Mac for things like DSL credentials, note all your network settings, because the latter steps will destroy them. If you got all the way to the last step, if things don't work any worse than before, you can trash the saved SystemConfiguration folder.
I had the same problem. It started when I temporarily turned off my filewall in Airport Express. When I turned the filewall back on, I would lose my WiFi connection anytime the computer would sleep.
When I went into System Preferences > Network and selected Wi-Fi and then clicked on the Advanced... button in the lower right corner, it showed my Network name but it said "None" in the right column under Security.
I highlighted network name and then clicked on the - button just below to delete the "Preferred Network". Then I clicked on the + button and added my network again.
Once I did that, it showed "WPA2 Personal" in the right column under Security. I suspect that's going to fix the problem, but I just did it so I can't say for sure until I've tested it for a couple of days.