hello, I have buttons in my master page that allow users to nevigate in the site without log in. I...

Question

hello,  I have buttons in my master page that allow users to nevigate in the site without log in.  I aso have a shopping cart page and I want to check if the user is log in or not once the user click on button to select products.  how can I do it?
 I've tried   if (HttpContext.Current.User.Identity.IsAuthenticated) Response.Redirect("~/CheckOut.aspx"); else Response.Redirect("~/Login.aspx", true);  
and it doesnt work.
 thanks.

p.s
what I mean is something like this site - if you want to write a post and you are not loged in it's redirect you to the login page.