This is preposterous, I've never had this before. I got this new external HDD that plugs into the USB and it's not being recognized. Huhuhu... Nothing happens. I put in my USB flashdisk and it mounts without a problem.
Same happened with my usb flashdisk once and it came out to be a hardware problem. I guess the same is in your case. Update us if you figured out the problem.
Please check your BIOS, maybe you need to upgrade, I am facing the same problem with my 1TB external HDD
The problem can be of cable also.. Check the HDD cable. I once had the same problem which was of cable fault.
Sometimes problem with the cable, try to test with another cable data. If still problem probably the system not identify, try to test on another computer.