Help me please

Help me please

i have downloaded JQuery and put into the same folder as the file i am working on and whatever i do JQuery will not work

here is my code

<script src="JQuery.js"></script>
        <script>
            function fadein(){
                var box = document.getElementById('light');
                box.style.display = 'block';
                $('box').fadeIn('slow');
                var black = document.getElementById('fade');
                fade.style.display = 'block';
            }
        </script>

i have looked at many different forums but i can not find a solution... if you can help it will be greatly appreciated