Edit in JSFiddle

<h3>Submit button should be enabled if at least one checkbox is checked</h3>

<form>
    <div>
        <input type="checkbox" name="op1" id="op1" /> <label for="op1">First Option</label>
    </div>
    <div>
        <input type="checkbox" name="op2" id="op2" /> <label for="op2">Second Option</label>
    </div>
    <div>
        <input type="checkbox" name="op3" id="op3" /> <label for="op3">Third Option</label>
    </div>
    <div>
        <input type="checkbox" name="op4" id="op4" /> <label for="op4">Fourth Option</label>
    </div>
    <div>
        <input type="submit" value="Submit Form" disabled />
    </div>
</form>

$("input[type='checkbox']").click(function() {
    $("input[type='submit']").attr("disabled", !$("input[type='checkbox']").is(":checked"));
});