Try connecting it to a different computer, to see if it gets recognized.
Is it still under warranty? If so, exercise the warranty.
Otherwise, disassemble the case, remove the "internal" hard-drive, and connect that drive as a "slave" drive in a desktop computer, to see if the USB-to-disk-drive interface inside the case is the problem, while the data on the disk-drive could be OK.
Answers & Comments
Try connecting it to a different computer, to see if it gets recognized.
Is it still under warranty? If so, exercise the warranty.
Otherwise, disassemble the case, remove the "internal" hard-drive, and connect that drive as a "slave" drive in a desktop computer, to see if the USB-to-disk-drive interface inside the case is the problem, while the data on the disk-drive could be OK.