Data Controls :: DropDownList SelectedIndexChanged Event Not Firing

I take drop down list control ,from below code i bind data into drop down list from database...

public void load() {
try {
string sCon = gv.constr;
MySqlConnection con = new MySqlConnection(sCon);
con.Open();
String s = "Select * from company";
MySqlCommand cmd = new MySqlCommand(s, con);

[Code] ...

I used to done select index change event on  drop down list bt it's not working... I want select index value of drop down list item into textbox....wat i do?

protected void drpOrg_SelectedIndexChanged(object sender, EventArgs e){
string sCon = gv.constr;
MySqlConnection con = new MySqlConnection(sCon);
con.Open();
String s = "Select companyid from companyuser where orgname='"+drpOrg.SelectedValue.ToString()+"'";

[Code] ....