Real quick: if you're ever working in ASP.NET and a page loads without any indication of an error other than there being 100% no content whatsoever, check the code in global.asax in that project. I had an application that did all sorts of nonsense in the application_start event, and due to an errant configuration file change, that code blew up.
And all we saw on the client was a completely blank page. Viewing the HTML source of any page in the app yielded markup exactly matching what we were seeing:
Fixing the error in the global file fixed the issue with empty the body tags showing up on every page in the app. I know that this is nothing astounding, but a frantic Google search late that night of this particular deployment yielded NOTHING about ASP.NET pages rendering empty body tags.
So if that ever happens to you, check global.asax. If that code is peachy, then feel free to freak out.