Thinking about it further, Hack&Lube is likely right that the problem with the external drive is a driver issue. Did you try your USB 2.0 ports as well? They would probably be black inside, rather than blue. Also, try a regular USB key, if it does't work then the issue might not be the drive at all.
Makes sense to take a look at that before buying a new HDD and enclosure. If you do g this route, you could just pick up one of these:
http://www.memoryexpress.com/Products/MX28004 and something like this
http://www.memoryexpress.com/Products/MX44004
Note: If you want a new drive for inside your laptop, this might not be the one you would want as it is slower. Although, I have heard good things about the performance of the Momentus Thin models, I have no direct experience with them.