MacBook Air - cannot connect to any wifi networks!

http://osxdaily.com/2011/07/22/wifi-dropping-in-os-x-lion-fixes/

Ive tried everything from this page and still my MacBook air (i5 core) refuses to connect to any wireless networks other than my iPhone tether. I bought it in the US andwas wondering whether there we're any other suggestions.

I'm running 10.7.3 and my router is the BT homehub 2 (sigh). I also have a d-link router and every other device in the house can see it and connect other than the air.

Any advice? Its like carrying a (light) brick!