Calling functions with keyboard shortcuts when program is in background

Question

When the program is in the foreground it works, however if it's in background it isn'T working. Help please!

private void Form1_KeyDown(object sender, KeyEventArgs e)
{
    if (e.Control && e.KeyCode.ToString() == "A")
    {
        Bitmap bm = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height);
        Graphics g = Graphics.FromImage(bm);
        g.CopyFromScreen(0, 0, 0, 0, bm.Size);
        pictureBox1.Image = bm;
    }
}