I've experienced this screen quite a bit in the course of learning extension development. In Chrome, right click, Inspect Element, and then go to Console. You'll find that the Tridion GUI logs some super basic events so that you can see how it's loading.
console.log("[whatever the name of the function is]");
When you refresh your gui, you'll find out which JS functions are executing and which aren't. If they aren't executing at all, then there's something wrong with your config. If they are executing, then you need to review the JS for errors.