关于C#磁盘读写操作，写的操作怎么都不行，求大神指点

用的下面这个程序
using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using Microsoft.Win32.SafeHandles;
using System.Windows.Forms;
namespace Zgke
{
    /// 磁盘扇区
    ///
    public class DriverLoader
    {
        private const uint GENERIC_READ = 0x80000000;
        private const uint GENERIC_WRITE = 0x40000000;
        private const uint FILE_SHARE_READ = 0x00000001;
        private const uint FILE_SHARE_WRITE = 0x00000002;
        private const uint OPEN_EXISTING = 3;         
        [DllImport("kernel32.dll", SetLastError = true)]
        private static extern SafeFileHandle CreateFileA(string lpFileName, uint dwDesiredAccess, uint dwShareMode, IntPtr lpSecurityAttributes, uint dwCreationDisposition, uint dwFlagsAndAttributes, IntPtr hTemplateFile);
  
      
        private System.IO.FileStream _DirverStream;
        private long _SectorLength = 0;      
        private SafeFileHandle _DirverHandle;
        ///
        /// 扇区数
        ///
        public long SectorLength { get { return _SectorLength; } }
 
        ///
        /// 获取磁盘扇区信息
        ///
        /// G:
        public DriverLoader(string DirverName)
        {
            if (DirverName == null && DirverName.Trim().Length == 0) return;
            _DirverHandle = CreateFileA("\\\\.\\" + DirverName.Trim(), GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, IntPtr.Zero, OPEN_EXISTING, 0, IntPtr.Zero);
            _DirverStream = new System.IO.FileStream(_DirverHandle, System.IO.FileAccess.ReadWrite);
            GetSectorCount();
        }        ///
        /// 扇区显示转换
        ///
        /// 扇区长度512
        /// EB 52 90 ......55 AA
        public string GetString(byte[] SectorBytes)
        {
            if (SectorBytes.Length != 512) return "";
            StringBuilder ReturnText = new StringBuilder();
            int RowCount = 0;
            for (int i = 0; i != 512; i++)
            {
                ReturnText.Append(SectorBytes[i].ToString("X02") + " ");
                if (RowCount == 15)
                {
                    ReturnText.Append("\r\n");
                    RowCount = -1;
                }
                RowCount++;
            }
            return ReturnText.ToString();
        }              
        ///
        /// 获取扇区数
        ///
        private void GetSectorCount()
        {
            if (_DirverStream == null) return;
            _DirverStream.Position = 0;
            byte[] ReturnByte = new byte[512];
            _DirverStream.Read(ReturnByte, 0, 512); //获取第1扇区
         
            if (ReturnByte[0] == 0xEB && ReturnByte[1] == 0x58)           //DOS的好象都是32位
            {
                _SectorLength = (long)BitConverter.ToInt32(new byte[] { ReturnByte[32], ReturnByte[33], ReturnByte[34], ReturnByte[35] }, 0);
            }
            if (ReturnByte[0] == 0xEB && ReturnByte[1] == 0x52)          //NTFS好象是64位
            {
                _SectorLength = BitConverter.ToInt64(new byte[] { ReturnByte[40], ReturnByte[41], ReturnByte[42], ReturnByte[43], ReturnByte[44], ReturnByte[45], ReturnByte[46], ReturnByte[47] }, 0);
            }
        }      
     
        ///
        /// 读一个扇区
        ///
        /// 扇区号
        /// 如果扇区数字大于分区信息的扇区数返回NULL
        public byte[] ReadSector(long SectorIndex)
        {          
            if (SectorIndex > _SectorLength) return null;
            _DirverStream.Position = SectorIndex * 512;          
            byte[] ReturnByte = new byte[512];
            _DirverStream.Read(ReturnByte, 0, 512); //获取扇区
            return ReturnByte;
        }
        ///
        /// 写入数据
        ///
        /// 扇区长度512
        /// 扇区位置
        public void WritSector(byte[] SectorBytes, long SectorIndex)
        {
            if (SectorBytes.Length != 512) return;
            if (SectorIndex > _SectorLength) return;
            _DirverStream.Position = SectorIndex * 512;
            _DirverStream.Write(SectorBytes, 0, 512); //写入扇区 
        }
       
        ///
        /// 关闭
        ///
        public void Close()
        {
            _DirverStream.Close();
        }    
    }
}