<button id="btnLogin" value="Start">Начать разговор</button>

$(document).ready(function () {

    $("#txtNickName").val("").focus();

    $("#btnLogin").click(function () {
        var nickName = $("#txtNickName").val();
        if (nickName.length <= 50 && nickName) {
            var href = "/home/index?user=" + encodeURIComponent(nickName);
            href = href + "&logOn=true";
            $("#YourNickname").text('Привет, ' + nickName + '!');
            $("#LoginButton").attr("href", href).click();
        }
    });

    $('#txtNickName').keydown(function (e) {
        if (e.keyCode == 13) {
            e.preventDefault();
            $("#btnLogin").click();
        }
    })

});

<a data-ajax="true" data-ajax-failure="LoginOnFailure" data-ajax-mode="replace" data-ajax-success="LoginOnSuccess"
 data-ajax-update="#container" href="/Home" id="LoginButton" style="visibility:hidden">Login</a>

$("#LoginButton").attr("href", href).click();

$("#btnLogin").click(function () {
        var nickName = $("#txtNickName").val();
        if (nickName.length <= 50 && nickName) {
            var url = "/home/index";
            var data = "user=" + encodeURIComponent(nickName) + "&logOn=true";
            $.ajax({
                type: "POST",
                url: url,
                data: data,
                success: function (html) {
                    $("#LoginPanel").toggle();
                    $("#container").append(html);
                    $("#YourNickname").text('Привет, ' + nickName + '!');
                    $("#NickName").text(nickName);
                    LoginOnSuccess(html);
                },
                error: function (msg) {
                    LoginOnFailure(msg);
                }
            });
        }
    });