I downloaded the barebone example of Twitter\'s bootstrap and customized it. I tested it locally (with WAMP server) and everything works perfectly, both the CSS and the JScr
In addition to the very useful suggestions by @dialex and @Darrell , I will add that if none of that works, you can review any code that you might be linking to, ie. via require ('page.php');, for duplicates. Duplicated .js links tend to cause these issues.