Welcome to WebmasterWorld Guest from 126.96.36.199
Is your members area protected to allow member only access, has media bot indexed your site, and where the ads working before and recently stoped?
Do you have the corrct code placed on your pages, it is easy to copy paste from Adsense control panel to you page and leave a section of code out.
If you go into your Adsense control panel does it show impressions for ad displays.
If you check out the above suggestions we will be able to offer further assistance.