$(function(){
    $("#txtres").attr("disabled", "disabled");
    $("#txtres2").attr("disabled", "disabled"); 
    $("#chknew").click(function () {    
        $("#txtres").attr("disabled", this.checked);
        $("#txtres2").attr("disabled", this.checked);          
    });
});

Demo:

http://jsfiddle.net/w2jtg1b9/1/

$(function(){
    $("#txtres").attr("disabled", "disabled");
    $("#txtres2").attr("disabled", "disabled"); 
    $("#chknew").click(function () {    
        $("#txtres").attr("disabled", !this.checked);
        $("#txtres2").attr("disabled", !this.checked);          
    });
});

Demo:

http://jsfiddle.net/w2jtg1b9/3/

$(function(){
    $("#txtres").attr("disabled", "disabled");
    $("#txtres2").attr("disabled", "disabled"); 
    $("#chknew").click(function () {    
        $("#txtres").attr("disabled", this.checked);
        $("#txtres2").attr("disabled", this.checked);          
    });
});

$(function(){
    $("#txtres").attr("disabled", "disabled");
    $("#txtres2").attr("disabled", "disabled"); 
    $("#chknew").click(function () {    
        $("#txtres").attr("disabled", this.checked);
        $("#txtres2").attr("disabled", this.checked);          
    });
});

Demo:

http://jsfiddle.net/w2jtg1b9/1/