You should not use runat="server"
in an ASP.NET MVC application. That's the first thing you should remove from your form
tag. If you don't want to use the built-in TextBoxFor
helper to generate an input field you could always write the markup directly:
<input type="text" name="username" value="<%= Model.UserName %>" />
but usually it is better to use the helpers as they will take care of things like validation and generate proper markup for you.