Private Declare Function ShowWindow Lib "user32" (ByVal hwnd As Long, ByVal nCmdShow As Long) As Long
Const SW_SHOWMAXIMIZED =  3 
Const SW_SHOWMINIMIZED =  2 
Const SW_SHOWNORMAL =  1 
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long

Private Sub UserForm_Click()
Dim hwnd As Long
hwnd = FindWindow("ThunderDFrame", Me.Caption)
Call ShowWindow(hwnd, SW_SHOWMAXIMIZED)
End Sub