Enable or disable textboxes based on a check

Question

I have been trying to get this to work for days, and everything i have read through google shows it should be right, so I have no idea what I am doing wrong, I have a simple checkbox. and once that is checked, i need two other textboxes to become visible or enabled, I dont care which. I am also not stuck on a checkbox, if something is easier I am all for it. 

HTML

<tr>

           <td>

               &nbsp;</td>

           <td style="height: 51px; width: 377px; font-weight: bold;">

               Project Completed?</td>

           <td>

               <asp:CheckBox ID="CheckBox_ProjectResults" OnCheckedChanged="CheckBox_ProjectResults_CheckedChanged" runat="server" Width="200px"></asp:CheckBox>

           </td>

       </tr>

             <tr>

           <td>

               &nbsp;</td>

           <td style="height: 51px; width: 377px; font-weight: bold;">

               End Date</td>

           <td>

               <asp:TextBox ID="TxtActualEnd" runat="server" Width="200px" autocomplete="off"></asp:TextBox>

           </td>

       </tr>

            <tr>

           <td>

               &nbsp;</td>

           <td style="height: 51px; width: 377px; font-weight: bold;">

               Results Folder</td>

           <td>

        <asp:FileUpload ID="attachmentFileUpload" runat="server" Width="320px"/>

       

           </td>

       </tr>




and here is the C# behind it 

protected void CheckBox_ProjectResults_CheckedChanged(object sender, EventArgs e)

        {

            if (CheckBox_ProjectResults.Checked == true)

            {

                TxtActualEnd.Enabled = false;

                attachmentFileUpload.Enabled = false;

            }

            else

            {

                TxtActualEnd.Enabled = true;

                attachmentFileUpload.Enabled = true;

            }

        }