If it shows up at all in disk manager it will show as a drive, but unpartitioned and not usable.
Did you say it shows up under my computer as a usb device and correctly Identified, if so try right clicking it and see if it will alow you to format it.
If the drive does not show up in either place, My computer and under disk manager, one of 3 problems:
(1) defective drive
(2) defective enclouser
(3) Problem with USB comunications to the drive.
For 1 and two you would need to try in a 2nd computer. If it works then it is a problem with your usb port, either data or the power supplied to the drive.
If it does not work in a 2nd computer, return or RMA the drive.
You could check the drive, but you would need to remove from enclocure and obtain a adaptor cable to go from the 1.8 in drive connector to a standard sata data/power connector and install directly into a computer using the internal sata port.