I have seen this in many cases when installing FCS over windows 2008 , issue that your 14 day history not displayed appropriately (see below) or you have empty bars .
well to fix this issue we have things we need to make sure of :-
1-apply FCS SP1 if you did not do so already
2- that the localhost and server name are located in local intranet zone
3- that our account and settings are registered correctly we should start the configuration wizard
4- that the reporting server working ok by trying to access http://localhost/reports using the same account we used in the wizard
and now we have the nice bars back again