If you have deleted any file from your hard drive accidentally just double click on the recycle bin in the Windows or trash on your Mac. If you recover files there just drag the file to the desktop. In Windows just right click on the file and select restore. The file will be restored to its original location. If you cannot find the file in the recycle bin or trash, check whether you have a backup or not. You may also contact your system administrator if your PC is on a network and they usually have regular backups. If you are not able to find your deleted file till now there is another option for you and that is data recovery software. You can use any of the commercially available data recovery software to get your lost file. When you delete any data from your computer, the hard drives does not erase the data completely until something else is overwritten on it. These applications will scan your hard drive to find the pieces of the deleted file. There is possibility of recovering your data through these applications. Operating these applications does not require any sound technical knowledge about computers. These application are very interactive and user friendly. You can easily operate these applications to find your lost data.
If your hard drive has been crashed, you can use the disk repairing utility that comes with the computer. Most of the PC manufacturers provide this drive recovery software. However, they have certain limitations such as this software will work only if you have installed this software before you experience the crash. If nothing of the above options work for you, you can send the hard drive to hard disk recovery specialist. They will disassemble the hard drive and recover the lost data and restore disk.