See that "Valid XHTML" link on your main page? There's a reason WordPress has that as one of the default links. If you click it, it will check your page and tell you everything that's wrong with it.
In your case, that's 75 Errors in your theme or content. Some of them may have the same causes (one error can cause dozens of validation problems), but it's virtually certain that nobody wants to look through your invalid code and try to tell you where the problems are. Valid code a) tends to work the way you expect and b) is a heck of a lot easier to debug when it doesn't.
Make your site valid.