How to start my Game from NiftyGUI Main Menu

Question

I am trying to start my game from a Main Menu class that implements NiftyGUI. I am using OpenGL (LWJGL) and Java. The problem is that I am never able to get the main menu to disappear and then start the game class, which is World.java.

The following is what I would usually do when I have no main menu.

package com.dev.voxy;

import com.dev.voxy.utilities.GLScreen;
import com.dev.voxy.world.World;


public class Main extends GLScreen {

public static int WIDTH = 1280;
public static int HEIGHT = 720;

private World world;

public static void main(String[] args) {
    Main main = new Main();
    main.GLScreen(WIDTH, HEIGHT, false, 60, "Voxy");
}

@Override
public void init() {
    world = new World();
}

@Override
public void update() {
    world.update();
}

@Override
public void dispose() {
    world.dispose();
}

That is my main class and extends GLScreen

import org.lwjgl.LWJGLException;
import org.lwjgl.Sys;
import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.DisplayMode;

import static org.lwjgl.opengl.GL11.*;
import static org.lwjgl.util.glu.GLU.gluPerspective;



public abstract class GLScreen {
protected static int SCREEN_WIDTH;
protected static int SCREEN_HEIGHT;
protected boolean FULL_SCREEN;
protected static int FPS = 60;
protected static String SCREEN_TITLE;

private static long lastFPS;
private static int lfps;
public static int fps;

public void GLScreen(int width, int height, boolean fullscreen, int sync,     String title) {
    this.SCREEN_HEIGHT = height;
    this.SCREEN_WIDTH = width;
    this.FULL_SCREEN = fullscreen;
    this.FPS = sync;
    this.SCREEN_TITLE = title;
    InitScreen();
}

public void InitScreen() {
    createWindow();
    InitGL();
    init();
    Run();
}


void createWindow() {
    try {
        Display.setFullscreen(FULL_SCREEN);
        Display.setTitle(SCREEN_TITLE);
        DisplayMode displayMode = new DisplayMode(SCREEN_WIDTH, SCREEN_HEIGHT);
        Display.setDisplayMode(displayMode);
        Display.create();
    } catch (LWJGLException e) {
        e.printStackTrace();
    }
}

void InitGL(){
    glEnable(GL_TEXTURE_2D);
    glShadeModel(GL_SMOOTH);
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClearDepth(1.0);
    glDepthFunc(GL_LEQUAL);

    glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);

    glViewport(0, 0, Display.getWidth(), Display.getHeight());
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    gluPerspective(67.0f, SCREEN_WIDTH / SCREEN_HEIGHT, 0.001f, 1000f);   //TODO watch coding universe video
    glMatrixMode(GL_MODELVIEW);

    glEnable(GL_DEPTH_TEST);


    lastFPS = getTime();
}

public abstract void init();

public abstract void update();

public static int getFPS() {
    int cfps;
    if (getTime() - lastFPS > 1000 && lfps != fps) {
        lfps = fps;
        fps = 0; //reset the FPS counter
        lastFPS += 1000; //add one second
        cfps = fps;
    } else {
        cfps = lfps;
    }

    fps++;

    return cfps;
}

public static long getTime() {
    return (Sys.getTime() * 1000) / Sys.getTimerResolution();
}

void Run(){
    while(!Display.isCloseRequested()){
        try{
            glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
            glClearColor(0, 0, 0f, 0f);
            glLoadIdentity();
            update();
            Display.update();
            Display.sync(FPS);
    }  catch (Exception e){
            e.printStackTrace();
        }
    }
    dispose();
    destroy();
}


public abstract void dispose();

public void destroy() {
    Display.destroy();
    System.exit(0);
}
}

And finally my World Class is below.

import com.dev.voxy.Main;
import org.lwjgl.opengl.Display;

import static org.lwjgl.opengl.GL11.glColor3f;
import static org.lwjgl.opengl.GL11.glLoadIdentity;


public class World extends WorldManager {

private Chunk chunk;

public World() {
    super(Main.WIDTH, Main.HEIGHT);
    init();
}

@Override
public void init() {
    chunk = new Chunk(0, 0, 0);
    setRenderStats(true);
}

public void update() {
    input();
    render();
}

public void render() {
    render3D();
    Translate();
    chunk.render();
    glLoadIdentity();

    if (isRenderStats()) {
        render2D();
        glColor3f(1, 1, 1);
        renderStats();
    }
}

@Override
public void dispose() {
    chunk.dispose();
    Display.destroy();
    System.exit(0);
}
}

The problem is that when I try and incorporate my Menu into this it never works. First I tried GameStates so that whenever the game state is GAME the nifty should no longer render but this causes the Window to close because nifty no longer keeps it open, so then I tried to have the loop be outside the MainMenu Class but that also did not work because I kept running into static/non-static errors which I could not figure out. Then my last idea was why not try and put the gameloop inside the MainMenu Class but try to stop the nifty render while I try to start the game, but that left elements of the nifty on the screen and the rest was blank and the World class did not render. The following are my current Main, MainMenu, GLScreen and MyScreenController and MainMenu.xml files The MyscreenController controls what happens when the respective buttons are pressed and the MainMenu.xml is the nifty xml file that lays out everything.

All relevant files and classes may be found at the following link, they are the current ones where I am trying to get the main menu working. The classes shown above show what I did to get ONLY the game part working in the first place, without a menu. LINK

To sum up, I can get my game working when there is not main menu and I can get my main menu working when there is no game, I have tried as many things I can think of but after 3 days I'm simply lost and would like any suggestion/recommendation or idea. I think I just can't figure out how to manage game states and the game loop when there is a main menu and a game, I was thinking maybe if there was a way to stop nifty completely then clear the screen then set OpenGL to 3D I can get my game rendered, this is what I was trying to do near the end but could not figure it out.

Thank you.