Please prepare a working enclosure of the same model with the same specifications to make sure the problematic unit is defective.

1. Check the power adaptor and make sure the power indicator light on the adaptor is on.
2. Check the USB cable and see if it is broken.
3. Check the HDD inside the enclosure to make sure the jumper is set to the MASTER position.
4. Check to see if the connections inside the enclosures are made properly.
5. Try using the rear USB ports on the motherboard instead of the front USB ports.
6. Check for motherboard compatibility issues.
7. Check for HDD compatibility issues.