sql server 2005 deleting problem

If it gives you an error, that is normally a clue.
If it doesn't, then you need to look at your data.

The chances are it is your data that is the problem. Does your book name contain any spaces or punctuation? If so, then it will muck up the SQL command. To avoid that (and accidental or deliberate SQL Injection attacks) use parametrized queries instead:

private void button1_Click(object sender, EventArgs e)
        {
            SqlConnection s = new SqlConnection(@"DataSource=.\SQLEXPRESS;AttachDbFilename=C:\Users\mm\Documents\Visual Studio 2008\Projects\LAS\LAS\mm.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");
            string delstring = textBox1.Text;
            SqlCommand com = new SqlCommand("DELETE bookInfo WHERE bookName=@BN", s);
            com.AddWithValue("@BN", delstring);
            s.Open();
            com.ExecuteNonQuery();
            s.Close();
        }