Hi
I've prepared 2 screens. On the second one You can see the html structure of a demo site, on first You can see Your site. As You can see in first case it's very messed up, which means that a html structure has been broken. If You have not changed anything in template files than it has to be one of the modules. Please check all modules with custom added content for validation errors. Look for unclosed html tags. This is most likely causing all Your problems.