How to have gridview to populate with data when page loads and filter when DDL has selection?

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C#3.5

ASP.NET4

I have a GridView that is databound. The data shows in the GridView fine without the DDL inplace.

Here is the GridView:

<pre><asp:GridView ID="GridView5" runat="server" AllowPaging="True" 
                        AutoGenerateColumns="False" CellPadding="4" 
                        DataSourceID="SqlDataSourceFiveYear" ForeColor="#333333" GridLines="None" 
                        style="text-align: center" Width="994px">
                        <AlternatingRowStyle BackColor="White" ForeColor="#284775" />
                        <Columns>
                            <asp:BoundField DataField="INST_ID" HeaderText="INST_ID" 
                                SortExpression="INST_ID" />
                            <asp:BoundField DataField="SHORTNAME" HeaderText="SHORTNAME" 
                                SortExpression="SHORTNAME" />
                            <asp:BoundField DataField="FTE2013" HeaderText="FTE2013" 
                                SortExpression="FTE2013" />
                            <asp:BoundField DataField="FTE2014" HeaderText="FTE2014" 
                                SortExpression="FTE2014" />
                            <asp:BoundField DataField="FTE2015" HeaderText="FTE2015" 
                                SortExpression="FTE2015" />
                            <asp:BoundField DataField="FTE2016" HeaderText="FTE2016" 
                                SortExpression="FTE2016" />
                            <asp:BoundField DataField="FTE2017" HeaderText="FTE2017" 
                                SortExpression="FTE2017" />
                            <asp:BoundField DataField="HC2013" HeaderText="HC2013" 
                                SortExpression="HC2013" />
                            <asp:BoundField DataField="HC2014" HeaderText="HC2014" 
                                SortExpression="HC2014" />
                            <asp:BoundField DataField="HC2015" HeaderText="HC2015" 
                                SortExpression="HC2015" />
                            <asp:BoundField DataField="HC2016" HeaderText="HC2016" 
                                SortExpression="HC2016" />
                            <asp:BoundField DataField="HC2017" HeaderText="HC2017" 
                                SortExpression="HC2017" />
                        </Columns>
                        <EditRowStyle BackColor="#999999" />
                        <FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
                        <HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
                        <PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" />
                        <RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
                        <SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" />
                        <SortedAscendingCellStyle BackColor="#E9E7E2" />
                        <SortedAscendingHeaderStyle BackColor="#506C8C" />
                        <SortedDescendingCellStyle BackColor="#FFFDF8" />
                        <SortedDescendingHeaderStyle BackColor="#6F8DAE" />
                    </asp:GridView>

Here is the SQL Data Source:

<pre><asp:SqlDataSource ID="SqlDataSourceFiveYear" runat="server" 
                        ConnectionString="<%$ ConnectionStrings:HotSpotConnectionString %>" 
                        SelectCommand="SELECT * FROM [FTE2018Total] WHERE ([INST_ID] = @INST_ID) ORDER BY [INST_ID]">
                        <SelectParameters>
                            <asp:ControlParameter ControlID="DropDownList1" Name="INST_ID" 
                                PropertyName="SelectedValue" Type="String" />
                        </SelectParameters>
                    </asp:SqlDataSource>

Here is the DDL:

<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" DataSourceID="DropDownDataSource" 
                    DataTextField="SHORTNM" DataValueField="INST_ID" AppendDataBoundItems="True"
                        style="font-weight: 700" Width="500px">
                        <asp:ListItem Text="All Institutions" Value="0" />
                    </asp:DropDownList>

Here is the DDL SQL Data Source:

<asp:SqlDataSource ID="DropDownDataSource" runat="server" ConnectionString="<%$ ConnectionStrings:HotSpotConnectionString %>"
    SelectCommand="SELECT [INST_ID], [SHORTNM] FROM [TableCOCINST] ORDER BY [INST_ID]"></asp:SqlDataSource>

When the page loads it shows the DDL with All Institutions Selected as the first item but no GridView showing all the Data. When I make the selection in the DDL only that data is shown. Which is good but I am trying to get all the Data to show in the Gridview before the DDL selects an item.

What am i missing? Is my value for the DDL wrong?

What I have tried:

I have tried to change the way the DDL value.