A very simple random problem-please help

Hi all
I wrote a simple code that should generate two different random numbers.
I designed a window in which I placed two labels and one button.
On the button click event the lebels should show two different numbers between 3-19.
the problem is when I click the button the two labels always show the same number when I use the "F11" to see the step by step happening inside the code the resault come out OK. why isn't it goes that way when I run(F5) the program???
the code goes somthing like that:

private void button1_click(....)
{
      dieRoller myRoll = new dieRoller();
         label1.text = myRoll.Roller().ToString();
         label2.text = myRoll.Roller().ToString();
}

Class dieRoller
{
    public int Roller()
{
       int randNum;
       Random roll = new Random();

         randNum = (int)(roll.NextDouble()*16)+3;
         return randNum;
}
}

what is wrong here???