What Do I do if the Smartware is No files to be backup when there are files to be backed up

I have run a backup, plug in a different wester digital drive in the usb to backup the same source drive then after that backup, try and run the backups again and it says not files to be backed up. 0 Files 0KB to be backuped. The support staff said the drive was damanged I think it is a software issue. Any suggestions or thoughts. Thanks