Running a a form from a form

I have 2 classes:

public class Form1 : System.Windows.Forms.Form
public class Form3 : System.Windows.Forms.Form
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Main() starts Form3 (simple yes, no label):

static void Main()
{
Application.Run(new Form3());
}
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For the YES button I have the other form I want to run and close the Form3.

private void YES_Click(object sender, System.EventArgs e)
{
Application.Run(new Form1);
Application.Exit();
}
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When I run this and press YES an error box pops up that says:

An unhandled exception of type 'System.InvalidOperationException' occurred in system.windows.forms.dll

Additional information: It is invalid to start a second message loop on a single thread. Use Application.RunDialog or Form.ShowDialog instead.
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When I try to use Form.ShowDialog it won't compile and says it needs an object.
When I try to use Application.RunDialog it says it is unaccessable due to its protection level.

What should I do?