Błąd podczas linkowania klasy

#pragma once

#include <iostream>
#include <string>
#include<map>
#include "GameScreen.h"
#include "SplashScreen.h"
#include "MenuScreen.h"



//Allegro Inits
#include <allegro5\allegro.h>
#include <allegro5\allegro_image.h>
#include <map>

#define ScreenWidth 800
#define ScreenHeight 600

class ScreenManager
{
private:
    ScreenManager();
    ScreenManager( ScreenManager const & );
    void operator =( ScreenManager const & );
   
    GameScreen * currentScreen;
   
    std::map < std::string, GameScreen *> screenDirectory;
   
public:
    ~ScreenManager();
    static ScreenManager & GetInstance();
   
    void AddScreen( std::string newScreen );
   
    void Initialize();
    void LoadContent();
    void UnloadContent();
    void Update( ALLEGRO_EVENT ev );
    void Draw( ALLEGRO_DISPLAY * display );
};

#pragma once

#include <allegro5\allegro.h>
#include <allegro5\allegro_image.h>
#include <allegro5\allegro_font.h>
#include <allegro5\allegro_ttf.h>
#include "FileManager.h"
#include "InputManager.h"
#include "ScreenManager.h"

class MenuManager
{
private:
    FileManager fileManager;
    InputManager input;
   
    std::vector < std::string > attributes;
    std::vector < std::vector < std::string >> contents;
   
    ALLEGRO_BITMAP * image;
    ALLEGRO_FONT * font;
    std::vector < std::string > items;
    std::vector < std::pair < float, float >> position;
    std::vector < std::string > menuLinks;
    std::pair < float, float > newImageSize;
    std::pair < float, float > imageSize;
   
    int align;
    int active;
    int itemColor;
    int itemNumber;
   
    void SetItems();
   
public:
    MenuManager( void );
    ~MenuManager( void );
   
    void LoadContent( std::string idMenu );
    void UnloadContent();
    void Update( ALLEGRO_EVENT ev );
    void Draw( ALLEGRO_DISPLAY * display );
};

#pragma once

#include <allegro5\allegro.h>
#include <allegro5\allegro_font.h>
#include <allegro5\allegro_ttf.h>
#include "GameScreen.h"
#include "MenuManager.h"

class MenuScreen
    : public GameScreen
{
private:
    MenuManager menu;
public:
    MenuScreen( void );
    ~MenuScreen( void );
   
    void LoadContent();
    void UnloadContent();
    void Update( ALLEGRO_EVENT ev );
    void Draw( ALLEGRO_DISPLAY * display );
};

#pragma once

#include<allegro5\allegro.h>
#include<vector>
#include"InputManager.h"
#include"FileManager.h"

class GameScreen
{
protected:
    InputManager input;
    FileManager fileManager;
   
    std::vector < std::string > attributes;
    std::vector < std::vector < std::string >> contents;
public:
    GameScreen();
    ~GameScreen();
   
    virtual void LoadContent();
    virtual void UnloadContent();
    virtual void Update( ALLEGRO_EVENT ev );
    virtual void Draw( ALLEGRO_DISPLAY * display );
}