In case files and directories are not listed in FTP please first make sure that your FTP client is configured to use passive mode.

You can find out how to set the passive mode setting on for some popular FTP clients here:

 http://www.siteground.com/tutorials/ftp/ftp_client.htm

There might be also another reason for this issue. All Siteground shared hosting servers are configured not to list more than 2000 files in a single folder. If you have uploaded more than 2000 files in a folder you can use only the File manager in cPanel to manage them.