IPad 3g No Longer Connect To Internet

all my other devices work fine and are connecting (including iphone, MacBook, girlfriends "new" ipad). Mine worked fine for months then suddenly, i get the wifi signal but in settings, you just see the spinning gear - not the check mark. When you try to open a web page, it just says "not connected to the internet".This is the second time this has happend with the 3rd generation ipad. I had an ipad 1 for years and no probs, then i upgraded to the new one and it stopped connecting after a month or two. PC World said they had a few people report the same problem so just gave me a refund. Bought a replacement new ipad at Apple and now the same thing has happened to that one.