Opening Form Diffrent to main Form

You cannot do it in a simple way, because -- look at your entry point ("main"): Application Run is called with your form; that defines which form is main. Its instance is returned as the static read-only (important!) property Application.MainForm. There is no API to switch the main form -- for a good reason!

My best believe: you should not do this, because it will confuse your user very well.

Nevertheless, if you're as crazy as I am and want to work around this limitation, you can do this! You should

1) Close your main form and go out of application loop.

2) Now, you need to call Application.Run again with different parameter (your different form). You should understand that it may require your different form to be closed and re-opened, then you may need to store (persist it) and completely restore its state. You need to write this code in your main method.

3) You may want to make this call conditional, otherwise you will not see

4) You may look Application.Run within your main, switching main form case to case.

5) You should provide an option to allow the user to "close application completely", because, considering item (4), you may run it forever. This can be done in menu item "Exit", for example, as closing a form is no longer supports complete termination of the application. You will need a static condition data field (only because your main is static).

I did it, out of curiosity.

Now, you need either to say "I don't need it" and accept my answer or write a code using my plan. Optionally, I would gladly write this code, if you convince me that this effort is welcome (better after you show some of your effort). In all cases, I agree to answer reasonable follow-up questions.

Again, I do not recommend doing it for real-life application!

Possibly something as simple as showing Form2 from with Form1's initialization, then hiding Form1 until Form2 closes?

Here's a dirty sample:

public partial class Form1 : Form
{
    public Form2 frm2 = new Form2();
    public Form1()
    {
        InitializeComponent();
        Hide();
        frm2.ShowDialog();
        Show();
    }
}

Form1 doesn't get a chance to be seen until Form2 closes.