I have just experience this weird problem. My MacBook Air would not get issues an IP address by a WiFi router make Tenda model 11n. It would only say that it got a self assigned IP address and had no Internet connection.
It would show up in wireless connections by MAC address. It would not show up in DHCP client list whatsoever.
I have tried rebooting both laptop and the router, I've tried changing WiFi channel, tried static IP, but nothing worked.