incrediBILL - 6:58 am on Mar 3, 2013 (gmt 0)

AdSense has to crawl your site before it'll start serving ads and it usually takes a few days to get the ball rolling. I manually open all the pages on a new site to make sure the AdSense code is executed and active when I start one.

Also make sure it's in your allowed sites list in your AdSense setup.