winform connect to the database always appear timeout

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C#

SQL-Server

Visual-Studio

, +

The ado.net with Winform technology found outside the network connection to the database is always prompt: Timeout expired. The timeout period elapsed or the server does not respond before the operation is complete.
sqlconnection resources have been released, and set the time to 0 connectTimeOut useless.

The emergence of new problems
Load data anomalies: System.Data.SqlClient.SqlException (0x80131904): Timeout expired connections. When trying to use the pre-login handshake confirmed that exceeds this timeout. This may be because the pre-login handshake fails or the server failed to respond. Try to connect to the server when the duration is spent - [Pre-Login] initialization = 16; handshake = 14997; ---> System.ComponentModel.Win32Exception (0x80004005): outdated wait operation.

My part of the code:

public static int ExecuteSql(string SQLString, params SqlParameter[] cmdParms)
 {
     SqlConnection.ClearAllPools();
     using (SqlConnection connection = new SqlConnection(connectionString))
     {
         using (SqlCommand cmd = new SqlCommand())
         {
             try
             {
                 PrepareCommand(cmd, connection, null, SQLString, cmdParms);
                 int rows = cmd.ExecuteNonQuery();
                 cmd.Parameters.Clear();
                 return rows;
             }
             catch (System.Data.SqlClient.SqlException e)
             {
                 SqlConnection.ClearPool(connection);
                 throw e;
             }
         }
     }
 }


 private static void PrepareCommand(SqlCommand cmd, SqlConnection conn, SqlTransaction trans, string cmdText, SqlParameter[] cmdParms)
 {
     if (conn.State != ConnectionState.Open)
         conn.Open();
     cmd.Connection = conn;
     cmd.CommandText = cmdText;
     if (trans != null)
         cmd.Transaction = trans;
     cmd.CommandType = CommandType.Text;//cmdType;
     if (cmdParms != null)
     {


         foreach (SqlParameter parameter in cmdParms)
         {
             if ((parameter.Direction == ParameterDirection.InputOutput || parameter.Direction == ParameterDirection.Input) &&
                 (parameter.Value == null))
             {
                 parameter.Value = DBNull.Value;
             }
             cmd.Parameters.Add(parameter);
         }
     }
 }