in first form just replace this in button_click event..
Session["DEMO_SESSION"] = txtname.Text;
Session["DEMO_SESSION1"] = txtpwd.Text;
Session["DEMO_SESSION2"] = txtpassword.Text;
Session["DEMO_SESSION3"] = txtadd.Text;
Session["DEMO_SESSION4"] = txtfull.Text;
Session["DEMO_SESSION5"] = DropDownList1.SelectedIndex;
Response.Redirect("default3.aspx");
Use this and don't forget to accept my answer...
Try it.. Best of luck.. :)