Show Dialog box at center of its parent

You might want to check the Form.StartPosition property.

http://msdn.microsoft.com/en-us/library/system.windows.forms.form.startposition.aspx

something along the lines of:

private void OpenForm(Form parent)
{
    FormLoading frm = new FormLoading();
    frm.Parent = parent;
    frm.StartPosition = FormStartPosition.CenterParent;
    frm.ShowDialog();
}

This of course requires setting the form’s parent.