Are you running any network services by any chance? (HTTP servers, network debuggers, etc)
Defold uses port 8002 for a web-based debugger, so there might be some conflict with that. Not sure if one can disable it or change the port to something else.
Also check if your loopback interface is working correctly (via ifconfig on linux/mac or ipconfig on windows).
This sounds like a privilege issue. Have you tried running the editor as administrator? Of course, you should be able to run the editor as a normal user, but knowing if it works as administrator would be helpful.