change screen problem

i try a gamesystem when i try change the gamestament the graphics of 3d model is very poor

and i don´t know how fix the problem

        public World(Game game, Manager ola, string text)
            : base(game)
        {

            NeoManager = ola;

            texto = text;
            System.Console.Write(texto);
            //   graphicsDeviceManager.PreferredGraphicsProfile = new FeatureLevel[] { FeatureLevel.Level_9_1, };
            pointer = new PointerManager(game);


            // this game system has something to draw - enable drawing by default
            // this can be disabled to make objects drawn by this system disappear
            Visible = true;

            // this game system has logic that needs to be updated - enable update by default
            // this can be disabled to simulate a "pause" in logic update
            Enabled = true;

            // add the system itself to the systems list, so that it will get initialized and processed properly
            // this can be done after game initialization - the Game class supports adding and removing of game systems dynamically
            Game.GameSystems.Add(this);
        }

 public override void Draw(GameTime gameTime)
        {


            NeoManager.BeginDraw(gameTime);the problem is where
            GraphicsDevice.Clear(SharpDX.Color.CornflowerBlue);
            model.Draw(GraphicsDevice, world, view, projection);

            /////GraphicsDevice.DepthStencilState = DepthStencilState.Default;
            ////  device.Clear();
            //// // Render the text
            spriteBatch.Begin();

            spriteBatch.DrawString(arial16BMFont, "Press the pointer to switch models...\r\nCurrent Model: " + model.Name, new Vector2(16, 16), Color.White);
            ////GraphicsDevice.Clear(Color.AntiqueWhite);

            //// GraphicsDevice.SamplerStates.Default;
            spriteBatch.End();


            //    GraphicsDevice.ClearState();

            NeoManager.EndDraw();// problem is cause by this 

            base.Draw(gameTime);

        
        }

   public Gamer()
        {
            // Creates a graphics manager. This is mandatory.
           
            graphicsDeviceManager = new GraphicsDeviceManager(this);
            graphicsDeviceManager.PreferredBackBufferWidth = 1280;
            graphicsDeviceManager.PreferredBackBufferHeight = 800;
            NeoManager = new Manager(this);           
            IsMouseVisible = true;
         
          //  _Login.Visible = true;

           // graphicsDeviceManager.IsFullScreen = true;
           // graphicsDeviceManager.re
          
            Content.RootDirectory = "Content";
     
  world = new World (this,NeoManager,"sa");
            
          
         

        }