does the drive show up in device manager when you right click on my computer and click manage? your drive might be mac formatted to work with that system, windows cannot see that format so what you can do is format the drive to NTFS so your windows can see it and get Paragon for mac or some similar software which basically gives your mac NTFS drivers so it can see the drive aswell
http://www.paragon-software.com/home/ntfs-mac/