How to Restore backup from external drive to itunes or iphone in Windows 8?
Solution 1:
iTunes doesn't work with symlinks very well. Try to copy the backup of your device back to "~\MobileSync\Backup" folder. Your backup is a folder in "Backup" folder with 40 random chars in name (device UDID).
After copying the backup, restart iTunes. It should now see the backup and allow you to restore it.