At the registrar, set the nameservers in the DNS options to
ns1.x10hosting.com
ns2.x10hosting.com
Then, add the domain as a parked domain in your cPanel
Download Joomla from http://www.joomla.org/ , then unzip the folder and upload using FTP.
Then just go to the install directory in your browser and follow the instructions (yourdomain.com/install)
it might be that the accounts are migrated to a new server, and everything hasn't been fully installed yet. If it's still the same after the migration is done, please let us know