You may have inadvertently created an infinite loop in your world constructor and construction of the world does not complete (leaving no world to display). If your 'Act/Run/Reset' buttons are inactive (dulled state), this is probably the case. If you can open your world class editor, comment out all but the 'super' call in the constructor and re-compile. If you cannot compile, go to the menubar and try 'Controls>Show Debugger' and click on 'Terminate'. If you are unable to do that, then go to your Task Manager and 'End Task' on the project and begin again.

Once you get your project back (and have full control of it), uncomment little by little what you commented out and compile after each section uncommented. If you run into the same problem as before, you know that the problem resides in the last part you uncommented.