vbFormControlMenu 0 The user chose the Close command from the Control menu on the form. 
vbFormCode 1 The Unload statement is invoked from code. 
vbAppWindows 2 The current Microsoft Windows operating environment session is ending. 
vbAppTaskManager 3 The Microsoft Windows Task Manager is closing the application. 
vbFormMDIForm 4 An MDI child form is closing because the MDI form is closing. 
vbFormOwner 5 A form is closing because its owner is closing.

If App.PrevInstance = True Then 'application is running
    'do something
Else                            'application is not running
    'do other
End If