If user has multiple screens,
how can I start application in primary screen or chosen screen at start up
See this MSDN question: http://social.msdn.microsoft.com/Forums/en-US/wpf/thread/316c001b-0511-4c18-8e26-d46021381ae6
You can find information about the primary screen in SystemParameters.PrimaryScreen* Then you can use Window.WindowStartupLocation or for a specific point you can use the W32 APIs and use SetWindowPos to position your screen on start up.