Enable and disable check boxes using ng-disabled

I got a list of check box + labels. If you check the first one, all the checkbox (except the first one) have to be disabled. The problem is that if I uncheck the first checkbox, all the others are still disabled and I want them to be enable again.

JS

<li ng-repeat="ques in questions">
        <input type="checkbox" ng-click="addRemove(ques)" ng-checked="contains(ques) != -1" ng-disabled="noneSelected && $index != 0"/> {{ques.question}}
</li>

controller

 if (ques.question == "None") {
            var index = $scope.contains(ques);
            if (index != -1) {
                $scope.noneSelected = false;
                $rootScope.selectedQuestions.splice(index, 1);
            } else {
                $scope.noneSelected = true;
                $rootScope.selectedQuestions = [];
                $rootScope.selectedQuestions.push(ques);
            }
 }