There is nothing worse than losing a file. What can you do if the worse happens? Can you ever retrieve that file?
If you delete a file, data recovery is possible, because it is only the file's entry in the index that has been deleted and not the file itself.
However, any further work you do on your PC may overwrite the file's location, so data recovery should be attempted as soon as possible.
Can I completely erase my hard disk?
You cannot entirely erase a hard disk (unless you really really know what you are doing!). Formatting does not place information beyond the reach of data recovery, which can even work on a disk that has been shredded. When every byte of information on a drive has been erased, it can sometimes be restored by using an ultra sensitive retrieval system.
How can I prevent this happening?
Make frequent backups
Store backups away from your PC
Ensure that backups works properly and will restore your system completely
Have a plan for retrieving lost information
What do I do if I lose information?
As soon as you encounter a problem stop what you are doing. Make a list of the last thing you did, the last application you used, recently installed software, the last upgrade etc. This will be useful if you have to seek assistance
Do not be tempted to make adjustments to your files or your drives
If you must work on something else on the drive, it may be possible to create a mirror (if suitable). Do not operate the original drive
Do not open the drive and attempt to repair it. A drive must only be worked on in a sterile atmosphere because even a tiny particle of dust can damage it
Handle the drive with the utmost care, ensuring that it is securely packed. A hard disk, particularly a defective one, can be further damaged by shocks and vibrations
So in short, there are a number of steps you can take if you lose data, but if you don't know what you are doing then get help!