i want to popup my form like message box when timer is done ?

Timer?! Do you want to keep your application running for years? :-)

You would rather need some service which creates a report sends what you need. Of course, you can develop appropriate Windows Service. Only a service will keep working when you log out, and even if you restart the system, it will be started, it you use start mode "Automatic" (http://msdn.microsoft.com/en-us/library/windows/desktop/aa384896%28v=vs.85%29.aspx[^]).

But Windows already provides the service designed for such things. It is already bundled with Windows and enabled; you can use it on different levels. It is called Window Task Scheduler, see http://en.wikipedia.org/wiki/Windows_Task_Scheduler[^].

First, you can schedule events using command-line utilities AT.EXE or CSHTASKS.EXE (which is replacing AT.EXE), see:
http://en.wikipedia.org/wiki/At_%28Windows%29[^],
http://en.wikipedia.org/wiki/Schtasks[^],
http://technet.microsoft.com/en-us/library/bb490866.aspx[^],
http://msdn.microsoft.com/en-us/library/windows/desktop/bb736357%28v=vs.85%29.aspx[^].

And you also can use Window Task Scheduler API, please see:
http://msdn.microsoft.com/en-us/library/windows/desktop/aa383614%28v=vs.85%29.aspx[^],
http://msdn.microsoft.com/en-us/library/windows/desktop/aa383608%28v=vs.85%29.aspx[^].

To see how can you use it with .NET, see this CodeProject article: A New Task Scheduler Class Library for .NET[^].

—SA

To display your Form center of the screen, set the Forms StartPosition property as CenterScreen on design timer on in your constructor.