Integrating external site fails

I am trying to integrate the osticket support system. While I looked there for help how to do it, I found some basic info that seems to work but not all the way.

What I did:
I included wp-blog-header.php and called get_header().

What works:
I can see the bar on the top with the user info of the admin account.
The background and everything is correct according to the template it should be.

What does not work:
– The title of the website is “page not found”. I have no idea where to change that.
– the menus only display the “Home” link, nothing else. I would like to have the full menu displayed
– The header image is missing. I am using the rotating image headers, not sure if that matter at all.

I am not sure what to do. Any help would be appreciated. You can look at it by going to https://uncovery.me/osticket

thanks!