Computer connected to network, but NO internet access

my computer says its connected to the internet but i have no access. ie, aim, slingbox all things that need internet connection do not work. ive tried all of the obvious solutions (pinging, clearing old internet file cookies etc.) i have this problem in multiple places with my laptop, at work, at home, friends houses and i cant connect to anything anywhere. i have tried lan connections and wireless. i made no changes in any of my settings, just one day it stopped working. please help if u can
thanks
matt