Well most of us will be using Google CDN jquery file. At times if the jquery file fail to load from the cdn network you can always load and use the local jquery file in  your server. Just use the following snipped

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.1/jquery.min.js"></script>

<script>window.jQuery || document.write('<script src="js/jquery-1.10.1.min.js"><\/script>')</script>