Hi, i need help with a little problem about 'Session'

Look at this piece of code:

<@ Page Language="VB" EnableSessionState="True" >

<script runat="server">

Dim st As String

Sub Page_Load()

st="computer"

Session("mystring")=st

End Sub


Sub bt_click(o As Object, e As EventArgs)

Dim st2 As String = Session("mystring")

tbox.Text=st2

End Sub


</script>


<form runat="server">

<asp:Button id="bt1" onclick="bt_click" Text="..." runat="server" />

<asp:TextBox id="tbox" runat="server" />

</form>



When I click the button I´d like to see the word "computer" in the textbox, but nothing appears.
What is wrong in this code ?
what I really want is have the changes made to st in the page_load sub, available in the bt_click sub.
Is there a way to do this without using Session ?

Thanks