Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Any) As Long
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function FindWindowEx& Lib "user32" _
Alias "FindWindowExA" (ByVal hWndParent As Long, ByVal hWndChildAfter As Long, ByVal lpClassName As String, ByVal lpWindowName As String)
Private Const WM_ENABLE = &HA
Private Const WM_SETTEXT = &HC
Private Const WM_ACTIVATE = &H6
Private Const WM_SETFOCUS = &H7

Private Sub Command1_Click()
Dim lhWnd As Long
Dim Fhwnd As Long
Fhwnd = FindWindow(vbNullString, "For")
lhWnd = FindWindowEx(Fhwnd,  0 , "Button", "Кнопка")

SendMessage lhWnd, WM_ENABLE,  0 , "1"

End Sub