How to loop bitmaps going down a form without using an array

Question

Hi there,

I would like to know how would I loop this piece of code once it has hit the bottom of the form?

Private Sub moveasteroid()
        'Asteroid 1
        If asteroiddown = True Then
            PictureBox1.Top += asteroidspeed
        Else
            PictureBox1.Left -= asteroidspeed
        End If
        If PictureBox1.Left + PictureBox1.Width > Me.ClientRectangle.Bottom Then
            asteroiddown = False
            PictureBox1.Top += asteroiddrop
        End If

Private Sub checkgameover()
        If PictureBox1.Top + PictureBox1.Width >= Me.ClientRectangle.Bottom And PictureBox1.Visible = True Then
            Timermain.Enabled = False
            MsgBox("Game Over- Region of space not protected!")
        End If

So once this ^ has happened, a box loads explaining the above, once the x is clicked how can I load this all over again? Could someone please explain using an example, this may help other beginners.

Thank you.