Check the output of "dmesg" after you plug the cable of the usb case. If it's recognized you should see something like:
usb 1-6: new high speed USB device using ehci_hcd and address 2
scsi1 : SCSI emulation for USB Mass Storage devices
usb-storage: device found at 2
Then you can manually mount it like this (assuming the hdd is ntfs formatted):
mount -t ntfs /dev/sda1 /mnt/hd
Note that the directory /mnt/hd must exist before mounting.
If the usb is not recognized then perhaps it's due to the bad hdd, since your usb stick is automatically detected.