Do you still need the 'original' home page for any reason?
Don't want to get too technical, but everyone has given you great support and told you how to fix it - however...
Please contact your hosting company and ask them the priority scheme of their index or home pages. There is a chance that your site defaults to index.html before it defaults to index.php. There is another issue as well. If your host is using Windows servers, then the htaccess file is meaningless.
Bottom line - first (if you do not need it) get rid of the index.html file. If you do not want to destroy it, just rename it - but when you rename it, make sure it doesn't automatically update its links (some apps like DreamWeaver and FrontPage will do that to you). The smart thing to do is rename it via your FTP application. Change it to index_old.html, for example. If the server supports php, then the home page becomes index.php and when someone enters the basic URL, it will go to that index page.
You have to trust us and your host, and work it out!
Respectfully,
John Underwood, jund