The nav bar is easy to corrupt and if you edit it directly rather then thru
web page options that's all the more likely to occur. Not to mention when
used with a site of that size. (have you considered breaking it up as
covered on http://www.publishermvps.com ?)
And hopefully you didn't use a Master Page, a sure sign of trouble.
What you'd have to do is go thru each page's web options dialog and uncheck
the page's option to be in the nav bar so that each page gets disconnected
from the nav bar wizard. When that's done you go thru each page and delete
the physical nav bar object off the page. When that's done you go to the
design gallery and pick a nav bar and insert it on page 1. That becomes your
new fresh nav bar wizard control. You then go thru each page and check the
page's option to be in the nav bar which then populates the nav bar wizard
with the page. When that's all done the nav bar on page 1 should display a
link for each page. You then copy the nav bar and then go thru the remaining
pages and paste it.

David Bartosik - [MSFT MVP]
www.publishermvps.com
www.davidbartosik.com