Hi and welcome to the WD community.
See if your hard drive is recognized on the Disk Management on Windows or the Disk Utility app for Mac. Check the link below for the steps. If the external hard drive is recognized, you should be able to use a data recovery program to recover your data, using Google you can find several options.
How to access Disk Management in Windows 7, Vista, XP or 2000 to manage your hard drives
http://wdc.custhelp.com/app/answers/detail/a_id/1284
How to access Disk Utility on a Mac computer
