loginname control

Hi
When i use code for users login
The loginname control that in masterpage not show username.
How i do?
if(Membership.ValidateUser(username,password))
{
// The credentials are correct, log the user in (create an authentication cookie)
FormsAuthentication.SetAuthCookie(username, false);

respons.Redirect("page.aspx")
}
else
{
// The credentials entered were invalid, display an error
}