per chiudere unapplicazione attiva fa così
codice:
Const WM_CLOSE = &H10

Declare Function FindWindowA Lib "user32" _
    (ByVal lpClassName As Any, ByVal lpWindowName As Any) As Integer
Declare Function SendMessageA Lib "user32" _
    (ByVal hWnd As Integer, ByVal wMsg As Integer, _
    ByVal wParam As Integer, lParam As Any) As Long
Function Kill(hWnd&)
    Dim Res& ' Ask it politely to close
    Res = SendMessageA(hWnd, WM_CLOSE, 0, 0)
    ' Kill it (just in case)
    Res = SendMessageA(hWnd, WM_DESTROY, 0, 0)
End Function
per esguire kill
codice:
Dim hWnd& '  window handle
    hWnd = FindWindowA(vbNullString, [NomeApp])
    Kill (hWnd)