Onclick of a button run code behind and do not postback the page(refresh) asp.net
<p><img src="http://i.stack.imgur.com/nvO8v.png" alt="enter image description here"><img src="http://i.stack.imgur.com/SMWgg.png" alt="enter image description here"></p>

<p>I have this issue of a drop down menu for my login. When I press the Log In link the drop down menu slides down. What I want is when <strong>wrong credentials</strong> are given to <strong>do not postback(refresh)</strong> so that the drop down menu will stay open for the user to type the correct password!</p>

<p>I have tried OnClientClick="return false;" but this disables the onclick event of my asp:button.</p>

<p>My code behind:</p>

<pre><code>string insCmd = "SELECT ID_USER FROM users WHERE username = @LoginEmail AND password = @passwd;";
        SqlCommand Login = new SqlCommand(insCmd, con);

        Login.Parameters.AddWithValue("@LoginEmail", txtLoginEmail.Text);
        Login.Parameters.AddWithValue("@passwd", txtLoginPassword.Text);

        try
        {
            SqlDataReader dr = Login.ExecuteReader();
            SqlDataReader dr2;

            if (dr == null || !dr.HasRows)
            {
                litErrorLogin.Text = "&lt;span&gt;Error:Wrong Credentials&lt;/span&gt;";

                //btnLogin.OnClientClick = "return false;";
                return;
            }

            while (dr.Read())
            {
                Session["UserID"] = dr.GetInt32(0);
            }
</code></pre>

<p>My html code:</p>

<pre><code>&lt;div id="bb_loginForm"&gt;
    &lt;div class="bg_loginForm"&gt;
        &lt;span style="font-size:11.5px;font-weight:bold"&gt;Log in to Account&lt;/span&gt; &lt;a class="bb_linkLoginHeaderHide" href="#" title="Hide"&gt;
            Hide&lt;/a&gt;
        &lt;br /&gt;
        &lt;div class="f_username"&gt;
            &lt;label for="txtLoginEmail" id="labelUser"&gt;
                Email
            &lt;/label&gt;
            &lt;br /&gt;
            &lt;asp:TextBox class="text-input" ID="txtLoginEmail" runat="server" Height="15px" Width="130px"&gt;&lt;/asp:TextBox&gt;
        &lt;/div&gt;

        &lt;div class="f_password"&gt;
            &lt;label for="txtLoginPassoword" id="labelPassword"&gt;
                Password
            &lt;/label&gt;
            &lt;br /&gt;
            &lt;asp:TextBox class="text-input" ID="txtLoginPassword" runat="server" Height="15px" Width="130px" 
                TextMode="Password"&gt;&lt;/asp:TextBox&gt;
        &lt;/div&gt;
        &lt;br /&gt;
        &lt;div class="f_login"&gt;

            &lt;!--src="../images/GreyButton.png"   class="submit btn primary-btn" onclick="btnLogin_Click"--&gt;
            &lt;asp:Button class="submit google-button" ID="btnLogin" onclick="btnLogin_Click" runat="server" Text="Log in" /&gt;                                       


            &lt;br /&gt;

            &lt;asp:CheckBox ID="chkRememberLogin" runat="server" /&gt;
            &amp;nbsp;
            &lt;label class="smaller" for="chkRememberLogin" id="labelrememberusername"&gt;Remember me
            &lt;/label&gt;
            &lt;br /&gt;
            &lt;a title="Forgot your login info?" href="#" class="underlineHover"&gt;Forgot your login
                info? &lt;/a&gt;
            &lt;br /&gt;
            &lt;asp:Literal ID="litErrorLogin" runat="server"&gt;&lt;/asp:Literal&gt;
        &lt;/div&gt;
    &lt;/div&gt;
&lt;/div&gt;
</code></pre>
