Anyone who's ever used a computer for any length of time has experienced the sensation of losing an important file through many reasons or injudicious use of the Delete key. Sometimes, though, what's lost can be found again.

If you accidentally deleted the file or the file lost
Steps:
1. Double-click on the Recycle Bin in Windows or the Trash on a Mac to see if the file is still there.
2. If you find the file, drag it to the desktop. To return the file to its original location in Windows, click on the file and select Restore from the drop-down menu.
3. If the file is no longer in the Recycle Bin or the Trash, look for a backup. If your PC is on a network that has regular backups, check with the system administrator to see if it's possible to retrieve a saved copy of the file.
4. Try using a commercial file-recovery utility that scans the disk for recognizable data, such as Data Recovery Wizard . When you delete a file, the operating system probably won't erase the actual bits from the disk until it needs them for something else; therefore, you may be able to recover some data.
5. If you decide to use a file-recovery utility, don't install it on the same disk that you're hoping to retrieve the file from, or you might overwrite the data you're trying to recover. Launch the software from a CD-ROM or a floppy disk. And if you download it directly from the Internet, don't download it onto the disk from which you deleted the file.

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If your hard disk crashed
Steps:
1. Try a commercial disk-repair utility, although success with these is somewhat limited if you didn't install the software before you experienced the crash.
2. If a disk appears to be irreparable and if the data is valuable enough, it's very important that nothing else is done to the drive - the best option is to power down and remove the drive from the machine. You can send the entire disk to a specialty drive-recovery service that will disassemble it and retrieve as much data as possible. Expect to pay at least a couple hundred dollars, though (payable even when they don't recover anything). Is backing up regularly starting to sound like a good idea?

Eventually, all hard drives crash. If you can't back up your entire drive, at least back up the data that you wouldn't want to lose forever.

Do some preventive measures. First, you have to make imaging of your bad hard disk onto a good one. This is your only way of keeping your hard disk's status on condition. If, somehow, you fail in your attempts to recover your disk, you still have a backup. So you would have chances to retry recovering another way.