The actual problem of the drive is the change in file structure.The mac OS uses HFS+ type and in win 8 its refs file system .A new structure designed for windows 8.The solution for your mac hard drive recovery problem is connect the drive to a windows 7 PC,format it with fat or extfat file system or some other common structure for win and mac .To restore the datas use this tool given below.IT is good in recovering datas from formatted windows and mac drive as well.
Perhaps, the drive file system is not compatible with each other. Therefore, you can try to format this drive on your Win8 PC and select a compatible file system.
If there is something important on this drive, you can try a free hard drive recovery program to get back your data before the format.
Note: You should keep this drive free from any new data before you recover all your data.
You should select a compatible file system before you start the format process in the “Format” interface.
You should always remember to back up your data frequently in case of data loss.