Do you have access to phpMyAdmin from the cPanel? This will give you access to the database where all the posts and all the other data is stored. A new WP installation probably created a new database, so that's why you're not seeing the old posts.
Once you're in phpMyAdmin, you'll see multiple databases in the left sidebar. Your original blog is probably _wrd1 or _wrdp1. Click into that database and you'll see the wp_posts table. All of your old posts should be inside this table. Before you do anything else, you should export the entire database to your local machine, so that you have a back up.
Now we need to get those posts back into your blog. But first, let us know if you've made it this far.