FPS camera problem

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Text;
 
using OpenTK;
using OpenTK.Graphics.OpenGL;
using OpenTK.Input;
using OpenTKGaem.GLUtilities;
 
namespace OpenTKGaem
{
    public class DirectionalCamera
    {
        public static DirectionalCamera dc = new DirectionalCamera ();
        Matrix4 View;
        Matrix4 Persp;
        Vector3 position;
        Vector3 up = new Vector3 (0.0f, 1.0f, 0.0f);
        float horizontalAngle = (float)Math.PI;
        float verticalAngle = 0.0f;
        float initialFoV = OpenTK.MathHelper.PiOver4;
        float speed = 3.0f;
        float mouseSpeed = 0.005f;
 
        public DirectionalCamera ()
        {
 
        }
 
        public void Init ()
        {
            position = new Vector3(0f ,0.0f, 10.0f);
            View = Matrix4.LookAt (position, Vector3.Zero, up);
            Persp = Matrix4.CreatePerspectiveFieldOfView (initialFoV, (float)Settings.width / Settings.height,
                                                     0.1f, 100.0f);
        }
 
        public void Update (float dt)
        {
            Vector2 hSS = new Vector2 (Settings.width / 2, Settings.height / 2);
            Vector2 mouseP = new Vector2 (((int)Game.g.Mouse.X), ((int)Game.g.Mouse.Y));
            Mouse.SetPosition (Game.g.X + hSS.X ,Game.g.Y +  hSS.Y);
 
            horizontalAngle += mouseSpeed * (float)dt * (hSS.X - mouseP.X);
            verticalAngle += mouseSpeed * (float)dt * (hSS.Y - mouseP.Y);
 
            Vector3 direction = new Vector3 (
                (float)(Math.Cos (verticalAngle) * Math.Sin (horizontalAngle)),
                (float)(Math.Sin (verticalAngle)),
                (float)(Math.Cos (verticalAngle) * Math.Cos (horizontalAngle))
            );
 
            Vector3 right = new Vector3 (
                (float)(Math.Sin (horizontalAngle - OpenTK.MathHelper.PiOver2)),
                0.0f,
                (float)(Math.Cos (horizontalAngle - OpenTK.MathHelper.PiOver2))
            );
 
            up = Vector3.Cross (right, direction);
 
            Vector3 dts = new Vector3 (dt * speed);
 
            if (Keyboard.GetState ().IsKeyDown (Key.W)) {
                position.X += direction.X * dts.X;
                position.Y += direction.Y * dts.Y;
                position.Z += direction.Z * dts.Z;
            }
 
            if (Keyboard.GetState ().IsKeyDown (Key.S)) {
                position.X -= direction.X * dts.X;
                position.Y -= direction.Y * dts.Y;
                position.Z -= direction.Z * dts.Z;
            }
 
            if (Keyboard.GetState ().IsKeyDown (Key.D)) {
                position.X += right.X * dts.X;
                position.Y += right.Y * dts.Y;
                position.Z += right.Z * dts.Z;
            }
 
            if (Keyboard.GetState ().IsKeyDown (Key.A)) {
                position.X -= right.X * dts.X;
                position.Y -= right.Y * dts.Y;
                position.Z -= right.Z * dts.Z;
            }
 
            View = Matrix4.LookAt (position, position + direction, up);
 
        }
 
        public void getMVP (ref Matrix4 MVP)
        {
            MVP = MVP * View * Persp;
        }
 
        public void getVP (out Matrix4 VP)
        {
                VP = View * Persp;
 
        }
    }
}