Try a different USB port on your computer. Try connecting it to a different computer. If it still is under warranty, then exercise the warranty. If not, disassemble the external case, and remove the disk-drive. Connect the disk-drive as a "slave" on some desktop computer, to see if the disk-drive is OK -- this implies that the USB-to-disk-drive adapter inside the case has failed.
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Try a different USB port on your computer.
Try connecting it to a different computer.
If it still is under warranty, then exercise the warranty.
If not, disassemble the external case, and remove the disk-drive.
Connect the disk-drive as a "slave" on some desktop computer, to see if the disk-drive is OK -- this implies that the USB-to-disk-drive adapter inside the case has failed.