you should try to check where the problem is comming from..
first check if you have an active internet connection..
if so are you behind a router of sorts?
then if you are all connected try to go to run in your start menu and type: cmd
(if you cant find run (for vista) do this: right click Start -> Properties -> Start Menu -> Customize. scroll down and there should be the run.. check it and click ok then it should be there)
there type:ipconfig /all
if you see ip adresses etc
then do this: ping www.google.com
if you get a reply report back here
if you need help report back and show us what reply's you got