We spoke with our host provider (ipowerweb.com) and they simply said that the SQL database was no longer on the server, as if it had been deleted. So we asked about backups, to be told that when a user deletes a SQL database, the backups are also deleted.
Great !
At least thanks to the Google cache of webpages, we have been able to recover most of the previous information. It does however, mean that you will need to register again.
Sorry for the inconvenience.