php md5 for login won't let me login, and keeps saying password incorrect -

the md5 posting database signup page know that's working, try here won't let me sign in , keeps telling me have wrong password.

 <?php  // parse log in form if user has filled out , pressed "log in" if (isset($_post["user_name"]) ) {          $user = mysql_real_escape_string($_post["user_name"]);               $pass_word = mysql_real_escape_string(md5($_post["pass_word"]));    $pass_word=md5($pass_word);      // connect mysql database       include "../connect_to_mysql.php";      $sql = mysql_query("select m_id member user_name='$user' , pass_word='$pass_word' limit 1"); // query person      // ------- make sure person exists in database ---------     $existcount = mysql_num_rows($sql); // count row nums     if ($existcount == 1) { // evaluate count          while($row = mysql_fetch_array($sql)){               $id = $row["m_id"];      }          $_session["m_id"] = $id;          $_session["user"] = $user;          $_session["pass_word"] = $pass_word;           header("location: ../../index.php");          exit();     } else {         echo 'that information incorrect, try again <a     href="member_login.php">click here</a>';          exit();     } } ?> 

you're running md5 twice on password.

$pass_word = mysql_real_escape_string(md5($_post["pass_word"])); $pass_word = md5($pass_word); 

also, don't use md5, unsafe, using bcrypt, secure, , easy implement in php. replacing md5 line of code make password hashes safe. preferably add salt, salt being random string. make breaking passwords nigh impossible.

$hash = password_hash($password . $salt, password_bcrypt);