Thank you for your post.
Check to make sure all necessary ports are open on both machines. I suspect port 443 is not open on the Web Server. For a complete list of ports that need to be open in FileMaker Server, see Knowledge Base Article #12120:
Also, can you confirm you are using Windows Server 2012, and not Windows Server 2012 R2? The latter configuration is not supported as many issues were reported during the testing of FileMaker Server and it could not be certified.