Dealing with data disasters
First - don't panic! Your data, or part of it, is probably still on the disk, but inaccessible to you because of some structural or internal damage. Most problems are a result of one of three things:
1. Internal damage to the drive or another relevant part can render the data inaccessible to you, although the data itself is uncorrupted.
2. The hard disk itself might be damaged and therefore not functioning properly.
3. The data files themselves might be damaged or corrupted.
Data recovery specialists are experienced in dealing with all three problems. So use the links above and find someone to help you.