How can I save alarm time & alarm file in windows service alarm clock that is developed in c# language at visual studio 2010

Of course you can do it. But, instead of developing your own service, why not using one which is already available and designed for such purposes?

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