Check the Application name should be "Discover" and your dgraph port number should be 15000. if you did not create the application with the above configuration it would better to recreate.
Which version OF endeca are u using?
Check whether the properties in Assembler.properties under \Endeca\ToolsAndFrameworks\3.1.2\reference\discover-electronics-authoring\WEB-INF\ are referring your current running MDEX application if not change the properties file accordingly.
Also check if you have the proper discover.xml file under \Endeca\ToolsAndFrameworks\3.1.2\server\workspace\work\Standalone
It should have
Are you working on windows or Linux...