Stop posting into more than one thread on any issue please. Your issue is completely different.
re: front page 404 (page not found) error
That error message can easily be addressed. Publish a post and it will be gone. By default the front page of your blog displays all posts (not pages) in reverse chronological order, with the most recently published post on top. The 404 (page not found) error message on the front page of the blog appeared because the Admin of the blog deleted the placeholder Hello World post. http://en.support.wordpress.com/not-found/
On the bottom of your Admin page you will find a link to the step by step Learn WordPress.com blogging Tutorial prepared by Staff. http://learn.wordpress.com/
The support documentation is all found at the Support link http://en.support.wordpress.com which is also on the bottom of your Admin page.