C# calling form.show() from another thread

Try using an invoke call:

public static Form globalForm;

void Main()
{
    globalForm = new Form();
    globalForm.Show();
    globalForm.Hide();
    // Spawn threads here
}

void ThreadProc()
{
    myForm form = new myForm();
    globalForm.Invoke((MethodInvoker)delegate() {
        form.Text = "my text";
        form.Show();
    });
}

The "invoke" call tells the form "Please execute this code in your thread rather than mine." You can then make changes to the WinForms UI from within the delegate.

More documentation about Invoke is here: http://msdn.microsoft.com/en-us/library/zyzhdc6b.aspx

EDIT: You will need to use a WinForms object that already exists in order to call invoke. I've shown here how you can create a global object; otherwise, if you have any other windows objects, those will work as well.

You should call Application.Run() after you call form.Show(). For example:

public void showForm() 
{
    // Do some work here.
    myForm form = new myForm();
    form.Text = "my text";
    form.Show();
    Application.Run();
    // Do some more work here
}

As for the details behind why, this msdn post may help.