Why Button Click Event doesn't work?

See more:

ASP.NET

Hi, please someone help me!
i searched alot for it but i couldn't find anything.
i have a button in a page but its click event doesn't fire.
in my page i just have number of textBox and label with this buton and in code behind i have :

protected void btnRegister_Click(object sender, EventArgs e)
   {
       string name = txtName.Text;
       string family = txtFamily.Text;
       int username =Convert.ToInt32( txtUserName.Text);
       int password = Convert.ToInt32(txtRptPassword.Text);
       string email = txtEmail.Text;

       string date = DateTime.Now.ToString();
       bool status = false;
       Membership mem = new Membership(date, status);

       int grpId = Convert.ToInt32(dpdGroup.SelectedItem.Value);
       CourseGroup group = DB.CourseGroups.Where(g=>g.Id==grpId).First();

       bool result = DB.Users.Any(u => u.UserName == username);
       if (group.NumberOfStd < group.Capacity)
       {
           if (result == false)
           {
               Student std = new Student(name, family, username, password, email);
               DB.Users.InsertOnSubmit(std);
               std.AddMembership(mem);
               group.AddMember(mem);
               mem.AssignStudent(std);
               mem.AssignGroup(group);

           }
           else
           {
               Student searchStd = (Student)DB.Users.Where(s => s.UserName == username).First();
               DB.Users.InsertOnSubmit(searchStd);
               searchStd.AddMembership(mem);
               group.AddMember(mem);
               mem.AssignStudent(searchStd);
               mem.AssignGroup(group);

           }
       }
   }