Putting the drive in an external enclosure was a good idea. Don't use any disk checking utilities that will write to the disk before you recovery your files or you'll risk losing them. Partition recovery software software should be safe to use. If the partition can be recovered you should be able to see your files.
I found this freeware. I've never used it before, so hopefully it will work. You'll need to figure out what caused this to happen, because it can happen again. It could have been a virus or the drive is going bad.
TestDisk - CGSecurity