Airport cannot detect an IP address from my wireless modum

Hi
I'm wondering if anyone could give me some suggestions regarding AirPort. I recently got wireless internet. However my housemate somehow managed to change the IP address while hooking up his wii. So neither of our laptops could connect to the internet.

He called up the service provider, and managed to get the settings returned to their original state using his laptop (which runs vista), meaning that he can again connect.

However my macbook still cannot find an IP address to connect wirelessly. I seem to have tried everything with no luck! Does anyone know why this is occuring?

Any help at all would be greatly appreciated!

Rachel

Basically the Wireless Modem should be set to DHCP (handing out the addresses) and the Airport settings in System Prefs/Network of MacBook should be set to "Using DHCP"