Main Menu (About Us, Contact, Blog etc) disappears when I go to the Blog Page

the url is AXxperts.com The WordPress guy who helps me said this was the problem

There appears to be a conditional statement or something not working right between the header.php and archive.php in 1.5.1 as the horizontal header that stays floating on top of the page does not load. The page I’m having the problem on is: http://www.axxperts.com/blog-single-author-big/ I have checked in all 3 of my browswers (Chrome, Firefox, IE9).