When you upload your files, make sure you use the correct directory. All the files that you want to be viewed from the web must be placed in the public_html directory, or if you are uploading to an addon domain, the files must be placed in the directory that corresponds to that domain.
Your main home page must be named index.html, index.htm or index.php for it to display. The webserver is case sensitive - so your home page must be named in lower case.
If you uploaded your files using FTP, make sure that you set the permissions on your files correctly so that they are world-readable. (0644 for files and 0755 for directories) Don't set the permissions of your files to 777.
If you are on a corporate network, behind a proxy server, or your ISP uses cacheing (most cable providers do) you may not see your changes instantly, as the old site is still being served to you by your provider. You can sometimes force an update in your browser by hitting CTRL and F5.