Selenium FindsBy not executing

I am using a PageFactory in Selenium to get the element on the page but it is always null. What am I missing ? I am getting a null reference exception as txtUser is always null.

I have create a base Page class.

 public class Page
    {
         static IWebDriver driver = new RemoteWebDriver(new Uri("http://localhost:7171/wd/hub"), DesiredCapabilities.Firefox());

        public static string CurrentURL { get { return driver.Url; } }

        public static ISearchContext Driver
        {
            get { return driver; }
        }
}

I have created a LoginPage class and a Helper class that creates a static instance of LoginPage class.

 public class LoginHelper
    {
        public static LoginPage LoginPage
        {
            get
            {
                var loginPage = new LoginPage();
                PageFactory.InitElements(loginPage, new RetryingElementLocator(Page.Driver,TimeSpan.FromSeconds(300)));
                return loginPage;
            }

        }
    }
    public class LoginPage 
    {

        [FindsBy(How = How.Id, Using = "JobLogPageContentPlaceHolder_UserName")]
        static IWebElement txtUser {get;set;}

   //This Works OK. It opens the browser and takes to login page
        public void GoToLoginPage()
        {
            Page.GoToPage(TestData.BaseURL + "Login.aspx");
        }

        public void LoginUser(string user, string pass)
        {
            if (txtUser != null) // This is always null
            {
                txtUser.SendKeys(user);
            }
            txtPassword.SendKeys(pass);
            loginButton.Click();
        }

I have written a test as below.

public void CanOpenApplicationAndLogin()
        {
            LoginHelper.LoginPage.GoToLoginPage();
            LoginHelper.LoginPage.LoginUser(TestData.UserName, TestData.Password); // This fails
            Assert.AreEqual(TestData.BaseURL + "UploadPO.aspx", Page.CurrentURL);
}