Displaying a calender after month and year are selected from a drop down

Hello everybody, I am new to ASP.NET.  I am attempting to do an assginment for my Web technologies class.  One part of the assignment wants us to create a drop down that displays months in numbers and another drop down that contains years.  Once a user selects a value from both drop downs, a calender is suppose to appear underneath so the individual can select the day they were born.  I am having trouble getting the calender to display.  It displays if i select each value, go to the next page, and then come back instead of appearing right after i select a value from both drop downs.  Below is my code behind that i created to try and display the calender.  So far i only have it written for when year is selected it will display because I am not sure yet how to do it for both.  I appretiate any help/tips, thank you.  


protected void DropDownListYear_TextChanged1(object sender, EventArgs e) { Calend ...