changed ISP and can't get Snow Leopard server to connect

Today I changed my ISP from Sky to BT Infinity. It was all installed ok, and i have easily got my macbook, ipad and iphone (yes, I know, Apple geek!) connected and online.

I have tried to do the same with my mac mini snow leopard server but haven't succeeded. I have updated the network connection and the Airport connects to the new network... all appears ok.

But, I can't get anything to work. Can't get online and can't see the mac mini in my network list on my macbook... also can't connect to the SL server from my macbook. 😕

Is there something special that I have to do so the SL server to make the change? Everything appears to be connected so I'm not really sure what to try next.... any help would massively appreciated!

thanks