Sometimes, you have to start over. If you edit your post too enthusiastically - or if you switch between Compose and HTML modes too much, while editing - you can corrupt the formatting. You can cause a cornucopia of symptoms, from messed up index pages, with dropped sidebars , to unreadable posts (and yes, pages). Even the old trick of doing nothing but toggling between Compose and HTML modes may not work, every time.
What Blogger won't tell you