button click event is not firing under validation control

Hi friends,
I have a screen to enter customer information.Here I am using the text boxes.
I added Required field validation for Textbox fields.
When I am using validation button click event is not firing.
When I am disable my validation , Button click event is working. Why? In my page i am using update panel also.
i copid my code below,  i have other fields also. i did the code in same way.
If i use update panel,  validations won't work. how can i do the server side/ client side validation for textbox controls.
 
<asp:Content ID="Content1" ContentPlaceHolderID="Cph1" Runat="Server"> <asp:UpdatePanel runat="server" ID="updatepnlnewcust" UpdateMode="Conditional"> <ContentTemplate> <tr align="right"> <td align="right" style="width: 170px" ><a ...