The retrieval of data can be a very delicate matter, not just in the process required to retrieve it but also in the information being recovered. If you have data stored on a storage medium like a hard drive but the drive has become inaccessible this could be for a number of reasons:

The Operating System may have become corrupt and not able to load, in turn this would stop you accessing any files stored on windows. (This is one of the easiest problems to recover).  
The Hard Drive itself could fail; certain sectors of the disk may become damaged leaving the HD useless. (This method is slightly more complicated to recover).  
The Drive may have come under some form of physical damage (Dropped) or perhaps Fire or Water damage. (This is the hardest instance where retrieval is necessarily).

If you are unfortunate enough to be in the category of ‘physical damage’ then the process is a bit more intricate.

It is likely that parts of the Hard Drive (The damaged components) will have to be removed, a working hard drive will then have to be stripped of the required components and fixed to the damaged drive.

The actual information retrieved can also be a very delicate matter depending on where the drive comes from (for example the contents of the drive could be from the police), the information contained on here would be classed as ‘sensitive’ or ‘confidential’ it is essential that the company guarantees privacy of all retrieved data.