Originally Posted by carnageX
One thing you could try before formatting or anything, is booting off of a Linux LiveCd such as Ubuntu, and seeing if it recognizes the drive. You could at least then try to back up any data before doing anything more with it.
+1 on that. ^
Or check your bios and makes sure the computer sees your usb hdd drive.
If so it will display the current size and number brand for your hdd.
Personally I would grab a windows 7 dvd and let the installer run a bit until you get the option to format.
If the installation stops and says it cannot be formatted because it is unrecognizable or damaged I would assume the drive is messed up.
Seek rma service if any remaining warrenty is left on it.