Add a command button (Command1) to your form and add the following code :

VB Code:
  1. Private Declare Function InvalidateRect Lib "user32" (ByVal hwnd As Long, lpRect As Long, ByVal bErase As Long) As Long
  2.  
  3. Private Sub Command1_Click()
  4.  InvalidateRect 0&, 0&, False
  5. End Sub