As phil22 said, flash drives are not very reliable. Regardless, a person should always store their important data on multiple forms of media. You can try to use a data recovery program to reconstruct it but flash drives are more difficult to recover data from in the event of hardware failure. Your final option is to take it some place such as Kroll OnTrack. They specialize in data recovery, but they are expensive. Figure a starting price would be at least $300, and you could expect to pay as much as $1,000 for something such as a flash drive.