There is a ‘debugging’ option in most browsers (F12, I think) that might help shed some light on this.
We hear reports like this from time to time and it’s often a JavaScript problem, or a problem with the page not loading completely. Sometimes it’s an error in the PHP, but most of the time, it’s a problem with the data that, when combined with the code from FreePBX, yields a page that isn’t able to be rendered. Because of caching, however, it is likely that once you get to here, you’re going to not be able to escape with “hard reloading” the page (either by shutting down your browser and restarting or using the “force reload” option in your specific browser.