Do you get any errors when you try to open it? What does it say about the drive and its partitions in Disk Management, would you post a screenshot? Here's how to access it: How to access Disk Management in Windows to manage hard drives.
You could try accessing it via Ubuntu Live USB/DVD, to see if it's properly recognized and if you can get to your files, or try data recovery software: http://www.tomshardware.co.uk/forum/id-1644496/lost-data-recovery.html.
Please let me know how everything goes.
Boogieman_WD