Button doesn't work in Asp.net?

I become really confused ! I want to design online shopping web site and I create new empty asp.net web site in visual studio 2013 with framework 4.5 and I write Register.aspx with the following code : http://ift.tt/1ccIhjm

and I have Register.aspx.cs with the following code : http://ift.tt/1HUpJOA but when I click on the button nothing happens it seems that registerBtn_Click is not called ! what can I do ? how can I fix this issues?