Over 300+ impressions but not even a single click, why?

Beginning of this month, i have got a facebook app from download section, which is similar to "your death date". Then i customize it and submitted to facebook, then try to monetize it with ppc ad (which i found from this page http://developers.facebook.com/adproviders/). Still now i got 300+ impressions, but not even a single click. Currently using two banner ad slots, one in top and another one in bottom. any suggestions?