How to display a GIF in a PictureBox using threads in C #?

I have two Windows Form , the main one has in the middle of the screen a PictureBox which in turn contains a GIF of an animation "loading". The idea is that when the second Form is activated the event load first load the method where I have the thread, then run all the remaining code (methods, etc) and at the end another method that changes the property visible to false . I explain myself with the code:

    private void FrmHijo_Load(object sender, EventArgs e)
    {     
       FrmPrincipal.Instancia.mCarga();
       /*---------------------Codigo-----------------------------*/
       FrmPrincipal.Instancia.mDefault();    
     }

This is the mCarga() method:

public void mCarga()
  {
      ThreadStart delegado = new ThreadStart(mostrasPTBX);
      Thread hilo = new Thread(delegado);
      hilo.Start();
      Cursor.Hide();
  }

This is the method the delegate points to:

public void mostrasPTBX()
  {
      FrmPrincipal.Instancia.ptbImagenCarga.Visible = true;
      FrmPrincipal.Instancia.ptbImagenCarga.BringToFront();
  }

And this is the mDefault method that only hides the PictureBox :

public void mDefault()
   {
      FrmPrincipal.Instancia.ptbImagenCarga.Visible = false;
      FrmPrincipal.Instancia.ptbImagenCarga.BringToFront();
      Cursor.Show();
   }

The problem is that when opening FormHijo and activating the event Load does not make visible the PictureBox simply hiding the Cursor as indicated in the same method, try to put a MessageBox in the mostrasPTBX() method and if you showed them to load the FormHijo . Another thing, try to do it wirelessly just call the method mostrasPTBX() within the method mCarga() but I still had the same problem. Probably the problem is foreign to the threads besides that I am relatively new programming. I hope you can help me thanks.