title: Can't open multiple windows in PyQt5
body: <p>so I've made several GUIs using the PyQt designer and I aim for each of them to link with eachother and for them to be able to open eachother. I have gotten the start up page to open up the home page, however when I click the respective buttons on the home page to open the other pages, it crashes my program. Any help would in fixing this would be greatly appreciated.</p>
  
  <p>My code is below:</p>
  
  <pre><code>import sys
  from PyQt5 import QtGui, QtCore, QtWidgets
  from StartupPage import Ui_StartupWindow
  from HomePage import Ui_HomeWindow
  from FoodPage import Ui_FoodWindow
  from ExercisePage import Ui_ExerciseWindow
  from ProfilePage import Ui_ProfileWindow
  
  class Startup(QtWidgets.QMainWindow, Ui_StartupWindow):
      def __init__(self, parent=None):
          super(Startup, self).__init__(parent)
          self.setupUi(self)
          self.NewEntryButton.clicked.connect(self.NewButtonHandle)
          self.ContinueButton.clicked.connect(self.ContinueButtonHandle)
          self.HomeP=Home()
  
      def NewButtonHandle(self):
          self.HomeP.show()
  
      def ContinueButtonHandle(self):
          self.HomeP.show()
  
  class Home(QtWidgets.QMainWindow, Ui_HomeWindow):
      def __init__(self, parent=None):
          QtWidgets.QMainWindow.__init__(self, parent)
          self.setupUi(self)
          self.FoodP=Food()
          self.ExerciseP=Exercise()
          self.ProfileP=Profile()
          self.exerciseButton.clicked.connect(self.ExerciseButtonHandle)
          self.foodButton.clicked.connect(self.FoodButtonHandle)
          self.profileButton.clicked.connect(self.ProfileButtonHandle)
  
      def ExerciseButtonHandle():
          self.ExerciseP.show()
  
      def FoodButtonHandle():
          self.FoodP.show()
  
      def ProfileButtonHandle():
          self.ProfileP.show()
  
  class Food(QtWidgets.QMainWindow, Ui_FoodWindow):
      def __init__(self, parent=None):
          QtWidgets.QMainWindow.__init__(self, parent)
          self.setupUi(self)
  
  class Exercise(QtWidgets.QMainWindow, Ui_ExerciseWindow):
      def __init__(self, parent=None):
          QtWidgets.QMainWindow.__init__(self, parent)
          self.setupUi(self)
  
  class Profile(QtWidgets.QMainWindow, Ui_ProfileWindow):
      def __init__(self, parent=None):
          QtWidgets.QMainWindow.__init__(self, parent)
          self.setupUi(self)
  
  if __name__ == '__main__':
      app = QtWidgets.QApplication(sys.argv)
      window = Startup()
      window.show()
      sys.exit(app.exec_())
  </code></pre>