This article is too short to display the intricacies of what happened. For people more interested in the exact reason why he didn't accept the millennium prize from the Clay Institute and the nature of his proof to some slightly more rigorous mention (although the full proof is readily available on arXiv), please read this phenomenal piece written by The New Yorker in 2006, found here: http://www.newyorker.com/archive/2006/08/28/060828fa_fact2