You've got a few issues. Lets start with the mouseover. The code for it (the $OL line) needs to be the very first thing right after the <body> tag. Not having it there will give you issues like you're experiencing.
Now, as for the navigation, there are a few issues. They're both in your own CSS. The first changes the color of the text, which makes it seem that the buttons have no text.
html, input, textarea
If you change the color to #000000; the text shows up again.
The second issue is that you have a <div> that places itself right over the section of the navigation, which makes you unable to click anything in that area. That is the <div> right at the end of the page
<div class="foot"> </div>
If you remove that, it should make it work again.
EPC Tutorials... We're here to help!
Offering custom integration services. Contact me here
* Not affiliated with EasyPHPCalendar or NashTech Inc.