All you have in that fstab is root ( / ) and swap. With the usb drive inserted from terminal do a
ls -l /dev/disk/by-uuid
That will first show you all drives currently available. The 2nd command will list the uuid of the available partitions. Figure out which uuid goes with the usb drive (compare the output of the 2 commands) and add it to the /etc/fstab.
UUID=???????????????? /mount/point /ext? defaults 0 0
My /etc/fstab for example.
# <file system> <mount point> <type> <options> <dump> <pass>
# / was on /dev/sda1 during installation
UUID=b64f54cf-73bf-4a4a-9f54-e4db137c3ed9 / ext4 errors=remount-ro 0 1
# swap was on /dev/sda5 during installation
UUID=f2fc22fc-5042-47d5-8365-6638bb1979b8 none swap sw 0 0
# data partition /dev/sdb2
UUID=22805acc-488c-4f4c-919d-5ad78fbed1aa /media/Data ext4 defaults 0 0
# usb hdd backup
UUID=f29d3b18-d700-41f4-bba0-0b63bb02176a /media/backups/hdd ext4 noauto,user 0 0
# usb fdd backuup
UUID=7ef1ce58-10fd-4768-aa85-e0d924cde941 /media/backups/fdd ext4 noauto,user 0 0
As mine is on laptop I have a script that runs every 30 seconds to mount the usb drives instead of mounting when plugged in. I don't take them with me when I run around.
*EDIT* Something else is messed up though because they should auto mount and be available through the file manager on Mint. Above is work around.