I remember running into this same problem when I first started using this technique.
Do you have any other <style type= or <script type= in the head of your document? If so, try making this drop down code the last thing before your </head>
Make sure you did not mess anything up in the CSS file.
Also, make sure all your code is done correctly - Make sure your "call" codes inside your drop down text are all referencing the correct "menu" number.
Here is an example of code from my site: - Plan Your Visit is just text generated from iweb. This code is what you have to add to make the .js you added work.
title="Plan_Your_Visit_-_Visitor_Information.html" onMouseover="dropdownmenu(this, event, menu1, '180px')" onMouseout="delayhidemenu()" href="Plan_Your_Visit_-_Visitor_Information.html"><span class="style_2">Plan Your Visit</span>
Here is a website I built that uses this code. http://www.shineandleeschristmastrees.com Feel free to check it out and look at the source code.
Hope this helps a little.