cannot go to url with FQDN

Hi, I just installed SAP NetweaverSR17.4 Java system. I can see my page when I goto the url with just the host name (eg: http://hostname:50000), but when I try the FQDN (eg:(http://hostname.domain.com), it says - "This page cannot be displayed). The system was installed mentioning "Set FQDN for SAP system" during install. Could someone help me understand why this would be caused, and how to fix it? Thanks