If the site was working but now the database is empty then something has happened to your database. As DrByte said previously you should ask your website host to check the database server.
Do you have a backup of your database? If so you can use phpMyAdmin to restore it. If not you could try talking to your host to see if they will restore the database for you. They probably won't though.
If you cannot get the database restored you will need to start again with a new one. To do this you will need to upload the zc_install files from the Zen Cart distribution and go through the installation process.
Regards,
Christian.




