It is always in your best interest to keep an emergency data recovery plan in place. It basically involves laying out detailed instructions manual for the process of retrieving inaccessible or deleted data from a hard drive. So that if situation arise you need not panic and simply proceed with the recovery procedure.
Hard disk crashes are common due to several reasons. Data can be lost due to regular wear and tear, physical failures, software errors, computer viruses, malicious software, visiting affected sites or by simply opening your email. Other threats like fire and electrical are also not uncommon.
It is possible to completely recover your important files if you follow a set procedure from the beginning. If a file is deleted, your operating system merely deletes the address of the file from memory. The actual file remains intact on the disk till you run shortage of space. If you are running shortage of space the old files that are deleted are replaced by new files.
File Allocation Table (FAT) maintains details of all the files on the hard drive at any point of time. You data recovery software scans through this table to locate deleted files. If you start the standard procedure of recovery immediately you can recover the lost files 99% of times.
Though the freeware software available can perform this task easily but if the lost files are of critical importance it is highly recommended that you immediately shut down the system and seek professional help from data recovery firms. As a simple mistake and damage the files and make it permanently irrecoverable.