Apple Airport Extreme

Hi there, I'm a bit of a noob to networking and the forums, so plz bear with me.

I am running a broadband connection through my aiport extreme base station. I have my desktop computer directly connected (by a wire) to the base station. I then have 5 other laptops wirelessly connected to the base station. I can get all of the computers to connect to the base station, but the internet does not work on any of the computers even though they are connected. I have had the network working perfectly before, so I know that it can work, I was just hoping someone could tell me how

cheers