I was transferring data from a USB hard drive to a Windows machine. This particular Windows box was running XP. Windows XP decided to crash. In the process, HexP did something to the drive and roughly 40GB of data was no longer accessible.
Formatting the drive was not the way to go. I used Data Doctor Recovery to scan the disk and recover the files. The software has an interesting demo feature. You can scan and see which files can be recovered but you can only recover those files if you pay for the license. At that point the cost of the software would be secondary to the hope of recovering lost files.