Top Portion of Site Disappears in IE7

I am working on a site and the header element is completely disappearing in only IE7 (it shows in IE6 and IE8). It shows for a second, then once the whole page is loaded, it disappears. I have no idea what could be causing this. The portion disappearing is the section I have included via PHP, but it still doesn't show when I actually insert it into the file, so I don't think that is the problem. Any help would be appreciated. I can post any code that would be helpful, but most of it should be able to be found through the view source or inspecting an element.

On a side note, my opacities aren't working in any version of IE either. I have them in a separate IE CSS document and am using the filte开发者_运维问答rs, so I am not sure why it is not working.

I figured it out. Apparently IE7 doesn't like negative z-index values and so was placing my background image over certain elements on the page that were above it in the HTML. Strange, but that's IE for you I guess.