In your solution you should have a file called Program.cs if you open it, it should have the following in it.
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
}
To change the form which opens as the start form change the line
Application.Run(new Form1());
where you change Form1 to the name of the form you want to open on application start.
So if I have a form called Parent1 and I want to have it open when my application starts I would have;
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Parent1());
}
Leave the rest of the file alone.