When User Login Success After Store UserName in session like below code
protected void btnlogin_Click(object sender, EventArgs e)
{Session["UserName"] = txtusername.Text;
}
Then Every page load check this session like below code
protected void Page_Load(object sender, EventArgs e)
{
if (Session["UserName"] != null)
{
}else
{
Response.Redirect("LoginPage.aspx");
}
Any Doubts let me know..