I'd put the hard disk into a new USB enclosure and retest.
Let me be clear. I am writing about an USB enclosure that is not powered by USB.
Bob
I have an external HDD enclosure with an external power supply. However, when I plug into one of the PC's USB ports (6 of them, and yes, I tried them all), I get the following error: "Power Surge On Hub Port - A USB device has malfunctioned and exceeded the power limit of its port. You should disconnect the device." To eliminate the possibility of the HDD being the problem, I tested it in another enclosure unit that is known to work, and by mounting it as an internal slave drive, and in both cases it worked fine. One thing I did notice, which may or may not be a factor, is the variance between the power supply for the unit in question, and the unit I used for testing:
Unit in Question -
Input: 120-240VAC, 50/60Hz, 0.5A
Output: 12V == 2A 5V == 2A
6 Pin Configuration: (2)+12V,(2)+5V,(2)Gnd
Test Unit -
Input: 120-240VAC, 50/60Hz, 2A
Output: 12V == 2A 5V == 2A
5 Pin Configuration: (1)+12V,(2)+5V,(2) Gnd
What would happen if one of the two +12V pins was removed from the unit in question?
Unfortunately, attempts to contact the seller have been fruitless, so this no longer seems to be an option. The documentation that came with this enclosure unit is limited and vague, and I can find no manufacturer markings on the unit or the box it came in to seek additional information and/or help.
Any insight or suggestions will be GREATLY appreciated.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic