Typically when the sidebar moves to the bottom it is because of some coding problems in a post. This happens when images are too wide for the post area, or when you paste something in from the web or from another program such as MS Word. Set your blog to display only one post per page (options > reading) and then go through them a post at a time to see which one is causing the problem.
My Navbar is not jumbled, but it covers up about 25% of my header. I tried to reload my header, change it’s dimensions, but nothing works. Whenever I am signed in, the blue navbar covers a part of my header.
When I’m not signed in, it looks perfect. It does the same thing in Firefox and IE7.