jordan says:
<div id="product" runat="server">
                    </div>
 you need to place above div outside the menu div like below
<div id="menu">
    <ul class="nav navbar-nav navbar-left">
        <li class="active">
            <asp:LinkButton ID="lnkAllProducts" CssClass="btn btn-block" Text="All Products"
                runat="server" OnClick="BindImages" />
        </li>
        <li>
            <asp:LinkButton ID="lnkBestSellers" CssClass="btn btn-block" Text="Best Sellers"
                runat="server" />
        </li>
        <li>
            <asp:LinkButton ID="lnkNewestAdded" CssClass="btn btn-block" Text="Newest Added"
                runat="server" />
        </li>
    </ul>
</div>
<br />
<br />
<br />
<div id="product" runat="server">
</div>