Class App
  Friend Shared F2 As Form2
  Friend Shared F3 As Form3
End Class

Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles MyBase.Load
  App.F2 = Me
  Dim F1 As New Form1()
  F1.ShowDialog()
End Sub
 
Private Sub Button1_Click_1(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles Button1.Click 
 
  App.F3 = New Form3() 
  App.F3.Show() 
  Me.Hide() 
 
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles Button1.Click 
 
  App.F2.Show() 
  Me.Hide() 
 
End Sub