[Xav]

First, load up the START button's click event handler. Then, use System.Random.

First, you create a new random object:

Dim r As New System.Random(Now.Millisecond)

Then, to choose a random number between 1 and 4:

Dim i As Integer = r.Next(1,5)

Note we use '5' and not '4'. This is because the upper bound is exclusive, so it means "everything below the upper number. This does not apply to the lower number.

Then, use a select case statement:

Select Case i

  Case 1
    Box1.BackColor = Color.Red
  End Case

  Case 2
    Box1.BackColor = Color.Blue
  End Case

Case 3
    Box1.BackColor = Color.Yellow
  End Case

  Case 4
    Box1.BackColor = Color.Green
  End Case

End Select

I think that's how you do it in VB. I'm more used to C#, so it might not be exactly how you do Select Case statements.