Are you using the adsense signup page?
http://www.google.com/adsense/g-app-single-1 Also, make sure your site meets all their current requirements, such as a certain age, (not sure about quantity of content), but you must have content, and your site can not solely be based around using it to profit from adsense. If they seen or suspected any of these then they would have declined you. But if you meet whatever there current criteria is then i would definitely look on their site and see if you can file a complaint or send a real person an email and see if you can get set up with an account or have them at least tell you why your being declined.