Vista - 2nd time connection problems

Hi

I may well be being an idiot(!) but regardless I was hoping someone may be able to guide me in the right direction..........

I have just bought a Dell XPS 1530 which runs on Vista Home

I am having a problem getting online.

This is exactly what's happening..............

I have a desktop which connects to a broadband connection via a network cable - this works perfectly everytime
When I first plugged this cable into my new laptop I successfully got online and installed a few drivers etc and all seemed well
I then tried out the built in wireless connection in my local coffee shop - I got the password from the waitress and again successfully got online

The problem is that I can't seem to connect to the internet through the same cable / wireless more than once !!

My laptop simply will not connect again at home and I've also found this to be true at the coffee shop - I've also been round a friends used their cable plugged it in - fine. Tried to use it again the next day and it wouldn't connect no matter what I tried

This is driving me nuts can anyone suggest what the problem is

I have installed AVG (free version) and also Zone Alarm - I did think maybe Zone Alarm if affecting my second time connection ? I have however run it for several years on XP with absolutely no probs

PLEASE HELP

thanks

Sid