Is your campaign active and ready to serve?
If your campaign is set to inactive, or you gave it an end date that has come and gone, it won't serve any impressions.
To check the start and end dates of your campaigns, go to the "Manage" -> "Campaigns" section of your dashboard and look at the information in your campaign table.
Take a look at some other ways to increase reach:Is your audience large enough?
Were all of your ads approved?
Are you using too many ads?
(Web Only) Are you including at least one of every banner size?