cvlcc
The method of restore will depend on the method you used to do the backup, so please advise how did you do the backup and where was it backed up to.
ie
If the restore was done using the default server manager backup and restore panel, then you use the same panel to do the restore.
If you did a backup to USB using the admin console menu, then you restore this after a clean install os sme OS, and during the first boot. When prompted you attach the USB Drive.
I'm guessing that your USB drive may not have mounted correctly and it has no backup on it at all. See the USB drive Howto. The USB drive may also not be formatted correctly.