Is the player_menu object being deleted or just hidden? This example I think captures your structure, and it works:
Qt Code: 
  1. #include <QtGui>
  2. #include <QDebug>
  3.  
  4. class PlayerMenu: public QDialog {
  5.     Q_OBJECT
  6. public:
  7.     PlayerMenu(QWidget *p = 0): QDialog(p) { }
  8. };
  9.  
  10.  
  11. class GameLogic : public QObject
  12. {
  13.     Q_OBJECT
  14.     PlayerMenu *player_menu; //the menu for the player
  15.  
  16.  public:
  17.     GameLogic(QString player_name, int num_of_AI, QWidget *parent = 0) {
  18.         player_menu = new PlayerMenu(parent);
  19.         player_menu->show();
  20.     }
  21.     ~GameLogic() { 
  22.         delete player_menu;
  23.     }
  24. };
  25.  
  26.  
  27.  
  28. class StartMenu: public QMainWindow {
  29.     Q_OBJECT
  30. public:
  31.     StartMenu(QWidget *p = 0): QMainWindow(p), gl(0) {
  32.         setCentralWidget(new QLabel("Main Window", this));
  33.  
  34.         gl = new GameLogic("dummy", 1, this);
  35.     }
  36.     ~StartMenu() {
  37.         delete gl;
  38.     }
  39. public slots:
  40. private:
  41.     GameLogic *gl;
  42. };
  43.  
  44. int main(int argc, char *argv[])
  45. {
  46.     QApplication app(argc, argv);
  47.  
  48.  
  49.     StartMenu m;
  50.     m.show();
  51.     return app.exec();
  52. }
  53. #include "main.moc"
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The reason I asked about your QPointer is that I think you wanted a QScopedPointer in order that it do the memory deallocation during destruction.