Edit in JSFiddle

 <div id="maindv">
        First name:
        <input type="text" name="fname"><br>
        Last name:
        <input type="text" name="lname"><br>
        <input type="checkbox" name="vegnonveg" value="Bike">I prefer a veg<br>
        <input type="checkbox" name="vegnonveg" value="Car">I prefer non-veg
        <br />
        Gender:<input type="radio" name="sex" value="male">Male<br>
        <input type="radio" name="sex" value="female">Female<br />
        I am having Car :
        <select name="cars">
            <option value="nocar">No Car</option>
            <option value="volvo">Volvo</option>
            <option value="saab">Saab</option>
            <option value="fiat">Fiat</option>
            <option value="audi">Audi</option>
        </select><br />
        <textarea rows="4" cols="50">
        Comment
    </textarea><br />
        <button type="button">
            Test Button</button>
        <input type="button" value="Test Input Button">
    </div>
    <hr />
    <input type="button" value="Toggle (Enable/Disable)" id="btnToggle">

$("#btnToggle").bind("click",function(){
   if($("#maindv input").prop("disabled")) 
       $("#maindv input,select,textarea,button").prop("disabled", false);
    else
        $("#maindv input,select,textarea,button").prop("disabled", true);
});