in program.cs file replace the following code
Application.Run(new Form1());
with, an instance of your start-up form, such as
Form1 frm1 = new Form1();
frm1.Show();
Application.Run();
*** now you can dispose the form without closing the application
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from time to time, you will be needing these codes:
Application.Exit(); <- to close the whole application
frm1.Close(); <- to close your current form window
frm1.Dispose(); <- to free memory resources, when form is shown modally. ^_^
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***good luck***