Nav bar disappearing/reappearing?

My colleague is complaining that the navigation bar on her site comes and goes. It's a pretty straight forward page, the nav is plain text links, so this is puzzling. The site was written in Dreamweaver CS3, she is using IE7, does this maybe have something to do with the browser cache?

This is the link: http://diabetespsychologist.com/

Thanks for any insight.

looking at the code I can tell this was made in DW, No-offence but your code is a mess....

For some reason you have a "sitemenu-container" which is empty and the menu occurs outside of this div...

I would consider using a unordered list for creating menus, with some simple CSS you can achieve some nice results and search engines tend to like lists (so i have been told).

check out listamatic (search in google) for some ways of creating CSS menus...

Also I noticed that your main text paragraphs falls between <div> tags rather than <p>. You have also used <h> tags to hide text, which is black hat techniques (although you haven't used it to stuff in keywords )

Also I noticed you offer a SEO service yet you don't seem to like using the <meta name="keywords" content=""> tag, seems abit strange...
As for the disappearing menu I am stumped...