You are doing some awfully weird things here..
- You are rendering your actors manually instead of adding them to the stage and letting stage do the rendering.
- You are adding a text button every time resize() is called.
- You are changing the filter on a texture every time resize() is called -- no reason to do that..
- You are allocating a lot of objects every time the Screen is shown. So if somebody opens your Game screen, and then returns to your Menu screen, all those objects are re-created, which can lead to some big issues. You are also loading Textures here; you should not be doing that every time the screen is shown, as it will lead to eventually running out of memory.
- You are creating a new Screen every frame that the ENTER key is pressed.. ? At the very least; you should only do this on keyDown input. Using isKeyPressed checks every frame.
- You have a syntax error in your "textButtonStyle" block of code. This probably won't even compile..
- For UI elements it's much better to use tables for layout instead of specifying absolute positions and using magic numbers
My suggestion would be to "start small." Write a game with LibGDX that doesn't rely on multiple screens. Maybe Pong or Tic-Tac-Toe. Get familiar with Scene2D UI just using the default skin.
Here is an example of a menu that uses the default skin and a Table for layout:http://www.java-gaming.org/topics/easy-way-to-click-an-image/29386/msg/269651/view.html#msg269651
You can see how simple the code for that looks:https://gist.github.com/mattdesl/5461944