The exact same thing is happening to me right now, no impressions are to be seen and no ads are displayed ! When calling Google support (18662GOOGLE), Mike the googler I spoke to said my account was being looked into by a specialist and that he didnt have access to the account.

According to him, the specialist will email me to give me more information however I have no information on why my account is in the hands of a specialist or how long it will take !!

Any ideas ?