Conditon statement for combo box control.

I am doing my window form project, in which I am using the combo box control.

private void button5_Click(object sender, EventArgs e)
{
con.Open();
if (comboBox1.SelectedItem.ToString() == "DOCTOR DETAILS")
{
Form2 f2 = new Form2();
f2.Show();
}
else if (comboBox1.SelectedItem.ToString() == "PATIENT DETAILS")
{
Form3 f3 = new Form3();
f3.Show();
}
else if (comboBox1.SelectedItem.ToString() == "OPTICAL DETAILS")
{
Form4 f4 = new Form4();
f4.Show();
}
else if (comboBox1.SelectedItem.ToString() == "FEEDBACK DETAILS")
{
Form5 f5 = new Form5();
f5.Show();
}
else
MessageBox.Show("no table is selected");
con.Close();
}

This is the code I have written when I debug it show form3,form4 and form5 but when I select the DOCTOR DETAILS in the combo box it doesn't show me the form1 instead it show message box that "no table is selected".
so anyone pls tell me what mistake I have made and how to rectify it.