If you try to use the Fully Qualified Domain Name to access reporting services then you will most probably be prompted for username password several times ending with an empty page.
In order to be able to access Reporting Services using FQDN you will need to perform the following actions:
1. Register a Service Principal Name (SPN) for the Domain User Account that Runs SSRS
Consider the following example:
sample computer name: reportsrv01
sample domain: example.com
sample domain account: example\ssrsuser
Then on the Domain Controller Server in a Command Prompt with Elevated Rights, you can Run as Administrator:
example 1: If SSRS are on port 80 (no need to specify 80 as it is the default http port):
Setspn -s http/reportsrv01.example.com example\ssrsuser
example 2: If SSRS are on any other port (i.e. 2430):
Setspn -s http/reportsrv01.example.com:2430 example\ssrsuser
2. Edit the RsReportServer.config File
On the Reporting Services server, in the virtual directory of SSRS, edit the "RsReportServer.config" file and locate the authenticationtypes section.
Then add /rswindowsnegotiate as the first entry in the authenticationtypes section.
The above step will actually enable NTLM.
For more information please visit this MSDN article.