Will you please try clearing your browser cache and cookies first and then view your blog again. If your browser version is outdated you can upgrade any browser version here.
Have you been copying and pasting any content into the blog? if so this can cause the problem you describe. Go to Settings > Writing and select “ ___ WordPress should correct invalidly nested XHTML automatically” and then scroll down and click “Save Changes.”
Now, starting with your latest post, open it in the editor, make one minor change such as adding a space and then deleting it, and then click “Update Post.” Check your blog and see if it is back to normal.
If it’s not, then look for an open HTML tag and close it. Check your blog again and see if it is back to normal. If it’s still “messed up” then open the next post and do the same thing post by post until it goes back to normal.
If you have been copying and pasting text from elsewhere without using either icon 5 or icon 6 in Row 2 of the visual editor, please see here so you know how to do this correctly in the future. http://en.support.wordpress.com/visual-editor/#pasting-text