At work we had the problem, that after reinstalling Windows two partitions where missing.
My colleague showed the the proper tool for this work:
http://www.cgsecurity.org/wiki/TestDisk
This tools has also a windows port so it was quite easy to scan the disks and detect, that the partitions were still on the disk, but somehow the partition table got mangled.
I take no guarantee if you use this program! Proceed on your own risk!