checkbox list to generate one textbox-Collection of common programming errors

So i have this checkbox list and im trying to generate a textbox when the MISC checkbox is checked.

                Laptop
                Label Printer
                Printer
                Fax Line
                PC
                MFD
                Phone Line
                Misc
            

ON my Cs page I have………

protected void chbxEquipmnt_SelectedIndexChanged(object sender, EventArgs e)
{
    if (chbxEquipmnt.SelectedValue == "Misc")
    {
        TextBox txt = new TextBox();
        txt.ID = "txtMiscCheckBox";
        Page.Form.Controls.Add(txt);
    }
}

debugging i have tried with Postback which continuously on returns the first check box that was checked…for example i checked laptop instead of Misc first, the value in the debugger always show me laptop. Im not sure if a simple loop to go thru the all the button clicks would help…..I’m fresh out of school and this is a career change for me so thanks for the patience