You won't find a driver because you don't need to install one, it's built in to Windows and is installed automatically when you plug the drive in to your PC (it's what's known as a "plug & play" device). It's a generic Microsoft driver that works for all external hard drives.
It may be that the Windows has failed to assign a drive-letter to it, and no drive-letter = invisible drive.
Take a look in Disk Management (If it's shown there it won't have it's usual name so look carefully), right-click and choose "Change Drive Letter & Paths" >> click "New". Select a letter and click "Next" (or "OK", can't remember exactly).