CODE:

// Form1.Designer.cs
namespace HashCalcate
{
    partial class Form1
    {
        /// 
        /// 必要なデザイナー変数です。
        /// 
        private System.ComponentModel.IContainer components = null;

        /// 
        /// 使用中のリソースをすべてクリーンアップします。
        /// 
        /// マネージ リソースを破棄する場合は true を指定し、その他の場合は false を指定します。
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows フォーム デザイナーで生成されたコード

        /// 
        /// デザイナー サポートに必要なメソッドです。このメソッドの内容を
        /// コード エディターで変更しないでください。
        /// 
        private void InitializeComponent()
        {
            this.button1 = new System.Windows.Forms.Button();
            this.openFileDialog1 = new System.Windows.Forms.OpenFileDialog();
            this.textBox1 = new System.Windows.Forms.TextBox();
            this.label1 = new System.Windows.Forms.Label();
            this.label2 = new System.Windows.Forms.Label();
            this.textBox2 = new System.Windows.Forms.TextBox();
            this.textBox3 = new System.Windows.Forms.TextBox();
            this.SuspendLayout();
            // 
            // button1
            // 
            this.button1.Location = new System.Drawing.Point(181, 12);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(75, 23);
            this.button1.TabIndex = 0;
            this.button1.Text = "ファイルを開く";
            this.button1.UseVisualStyleBackColor = true;
            this.button1.Click += new System.EventHandler(this.button1_Click);
            // 
            // openFileDialog1
            // 
            this.openFileDialog1.Filter = "すべてのファイル(*.*)|*.*";
            this.openFileDialog1.FileOk += new System.ComponentModel.CancelEventHandler(this.openFileDialog1_FileOk);
            // 
            // textBox1
            // 
            this.textBox1.Location = new System.Drawing.Point(13, 12);
            this.textBox1.Name = "textBox1";
            this.textBox1.Size = new System.Drawing.Size(162, 19);
            this.textBox1.TabIndex = 1;
            // 
            // label1
            // 
            this.label1.AutoSize = true;
            this.label1.Location = new System.Drawing.Point(13, 38);
            this.label1.Name = "label1";
            this.label1.Size = new System.Drawing.Size(28, 12);
            this.label1.TabIndex = 2;
            this.label1.Text = "MD5";
            // 
            // label2
            // 
            this.label2.AutoSize = true;
            this.label2.Location = new System.Drawing.Point(13, 72);
            this.label2.Name = "label2";
            this.label2.Size = new System.Drawing.Size(34, 12);
            this.label2.TabIndex = 3;
            this.label2.Text = "SHA1";
            // 
            // textBox2
            // 
            this.textBox2.Location = new System.Drawing.Point(15, 50);
            this.textBox2.Name = "textBox2";
            this.textBox2.ReadOnly = true;
            this.textBox2.Size = new System.Drawing.Size(241, 19);
            this.textBox2.TabIndex = 4;
            // 
            // textBox3
            // 
            this.textBox3.Location = new System.Drawing.Point(12, 87);
            this.textBox3.Name = "textBox3";
            this.textBox3.ReadOnly = true;
            this.textBox3.Size = new System.Drawing.Size(241, 19);
            this.textBox3.TabIndex = 5;
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(270, 117);
            this.Controls.Add(this.textBox3);
            this.Controls.Add(this.textBox2);
            this.Controls.Add(this.label2);
            this.Controls.Add(this.label1);
            this.Controls.Add(this.textBox1);
            this.Controls.Add(this.button1);
            this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedSingle;
            this.MaximizeBox = false;
            this.MinimizeBox = false;
            this.Name = "Form1";
            this.Text = "ハッシュ値計算";
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private System.Windows.Forms.Button button1;
        private System.Windows.Forms.OpenFileDialog openFileDialog1;
        private System.Windows.Forms.TextBox textBox1;
        private System.Windows.Forms.Label label1;
        private System.Windows.Forms.Label label2;
        private System.Windows.Forms.TextBox textBox2;
        private System.Windows.Forms.TextBox textBox3;
    }
}

CODE:

// Form1.cs
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.IO;
using System.Security.Cryptography;
using System.Windows.Forms;

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

        private void button1_Click(object sender, EventArgs e)
        {
            openFileDialog1.ShowDialog();
        }

        private void openFileDialog1_FileOk(object sender, CancelEventArgs e)
        {
            textBox1.Text = openFileDialog1.FileName;
            textBox1.ReadOnly = true;
            try
            {
                using (var fs = new FileStream(textBox1.Text, FileMode.Open, FileAccess.Read, FileShare.Read))
                {
                    var md5 = new MD5CryptoServiceProvider();
                    byte[] bs = md5.ComputeHash(fs);
                    md5.Clear();
                    textBox2.Text = BitConverter.ToString(bs).Replace("-", "");

                    var sha1 = new SHA1CryptoServiceProvider();
                    byte[] bs2 = sha1.ComputeHash(fs);
                    sha1.Clear();
                    textBox3.Text = BitConverter.ToString(bs2).Replace("-", "");                    
                }
            }catch(Exception ex)
            {
                MessageBox.Show(ex.Message, "エラー", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }
    }
}

CODE:

// Program.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;

namespace HashCalcate
{
    static class Program
    {
        /// 
        /// アプリケーションのメイン エントリ ポイントです。
        /// 
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}