asp.net textbox empty on postback : I am trying to create a login page, however whenever i click on login button username textbox's text becomes empty.<br>
I have tried :<br>
1. Using Updatepanel didnt work<br>
2. OnClientClick- it doesnt fires OnClick event<br>
3. I tried getting value by string usrnm=Page.Request.Form["username"].ToString();
   but it gave null value<br>
4.I tried putting AutoPstBack="true" on textbox <br>

Heres by markUp:

     <label for="username">Username</label>
                                    <%--<input type="text" name="Uname" id="username"/>--%>
                                    <asp:TextBox ID="txtusrnm" runat="server" AutoPostBack="true"/>
                                </div>
                                <div class="form-group">
                                    <label for="password">Password</label>
                                    <input type="password" name="Pname" id="password">
                                </div>
                                <div class="form-group"><a href="#">Forgot password?</a></div>
                                <hr class="hr-sm hr-stroke" />
                                <div class="form-group">
                                    <%--<input id="btnlogin" type="button" class="btn btn-primary btn-wide" value="Login" runat="server" onserverclick="btnlogin_ServerClick"  >--%>
                                    
                                            <asp:Button ID="btnLogin" runat="server" Text="Login" class="btn btn-primary btn-wide" OnClick="btnLogin_Click" UseSubmitBehavior="false" EnableViewState="true" />