airport or router preventing macbook from connecting to internet

[goodmanx]

my friend has a bright, shiny, spanking new 15" macbook pro running os10.6.3 on which she's unable to connect wirelessly via the airport card; it connects fine via ethernet. the airport preference tells us that "AirPort has the self-assigned IP address 169.254.xxx.xx and will not be able to connect to the Internet ..." or "the airport is turned on but is not connected to the internet." a pc in the house does connect wirelessly to that network. our iphone does not connect to her network, either, using the same password. her carrier is at&t/u-verse using a 2wire modem/router, mdl. 2701hg-b.

we have power-cycled the computer and the router, turned on internet sharing (irrelevant to this issue?) and deleted from Mac/Library/Preferences/SystemCon?guration these files (per an old macrumors forum response re the same issue):
Com.apple.airport.prefrences.plist
NetworkInterfaces.plist
Preferences.plist

we'll appreciate any assistance.

[deckeda]

Unless you have a reason to suspect the various prefs files are corrupt I wouldn't bother trashing them: They aren't often a problem. Turn off Internet Sharing. Doubtful it's the problem here but it's a variable that doesn't need to exist.

Take a look at the DNS address or addresses entered on the Mac. Depending on how you have the router and 2Wire modem setup, you're either gonna need the 2Wire's address in there, the router's, maybe AT&T's or nothing at all.

So maybe take a look at the PC's settings and use those.

And why would a "brand-new" Mac only be running 10.6.3? It isn't current.

[C(-)ris]

Might be a wireless security settings issue. There are some scheme's that Macs just don't like. Try setting the wireless to a WPA2 security and make a new passphrase.

[modelamac]

The airport card in the Mac is not patient enough. You need to set up the router to broadcast a signal, which you have done (PC sees it). Then do the diagnostics/troubleshoot and use "apply".

I had that problem when we were traveling this past fall. The motels had routers where the signal strength varied all over the place, and my MB couldn't hold onto some very long. It would then self-assign an IP. It would take me forever, with a lot of fussing to get settled where I got online.