Losing my textbox.text property when clicking a button control!!!

Here is my markup:

<asp:Table ID="tblCollateralTable" BorderColor="DarkGray" BorderStyle="Groove"
BorderWidth="1px" CellPadding="1" CellSpacing="0" Font-Bold="true"
Font-Names="Tahoma" Font-Size="8pt" ForeColor="Blue" Width="900px& ...