SqlConnection.Open抛出异常C＃

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试图在C#中创建登录表单，连接到SQL server。但它一直在cn.Open();上抛出异常。我为我的SQL Server使用XAMPP。SqlConnection.Open抛出异常C＃

using System; 
using System.Collections.Generic; 
using System.ComponentModel; 
using System.Data; 
using System.Drawing; 
using System.Linq; 
using System.Text; 
using System.Threading.Tasks; 
using System.Windows.Forms; 
using System.Data.Sql; 
using System.Data.SqlClient; 

namespace BlackLight_CSharp 
{ 
    public partial class Form1 : Form 
    { 
     public Form1() 
     { 
      InitializeComponent(); 
     } 

     private void Form1_Load(object sender, EventArgs e) 
     { 

     } 

     private void button1_Click(object sender, EventArgs e) 
     { 
      SqlConnection cn = new SqlConnection("server=localhost;user id=root;database=blacklight_login"); 
      cn.Open(); 
      SqlCommand cmd = new SqlCommand("SELECT * FROM login WHERE Username= '"+txt_user.Text+"' AND Password = '"+txt_pass.Text+"'", cn); 
      SqlDataReader dr; 
      dr = cmd.ExecuteReader(); 
      int count = 0; 
      while (dr.Read()) 
      { 
       count += 1; 
      } 

      if (count == 1) 
      { 
       MessageBox.Show("OK"); 
       dashboard dash = new dashboard(); 
       dash.Show(); 
      } 
      else if (count > 0) 
      { 
       MessageBox.Show("Duplicate Username and Password"); 
      } 
      else 
      { 
       MessageBox.Show("Incorrect Username or Password, Try again."); 
      } 

      txt_user.Clear(); 
      txt_pass.Clear(); 
     } 
    } 
}

下面是错误的屏幕截图，