What do you mean by “lost files”? Do you accidentally delete them from your memory card or drive?
If that is true, you should immediately stop saving new file on this memory card or drive in case of data loss.
And then, you need a data recovery tool to restore them back. I know there is a free data recovery tool that works well on a drive and memory card. Importantly, it also helped my friend retrieve his data from a drive successfully. It is really worth a shot: http://blog4mark.blogspot.com/2012/12/deleted-files-rec...
Note: You are supposed to be more careful before you do any change to your important data. In my opinion, the best way for you is to back it up all the time.
Ways to recover files for Android phone
There are two ways by which one can get back deleted files. They are
1. Deleted files can be recovered from computer if it is able to detect android device as a drive. If not then it is required to recover it with a data recovery program. If computer can read it then it is enough. Steps to recover for Android with data recovery
• Connect the device with the computer system.
• Put the USB connect mode as USB mass storage.
• It will display details about the device such as device model, serial number and SD card capacity.
• Click the “start” button to scan device for deleted images or photos, videos, songs and movies.
• After scanning, all recoverable files are classified into different file types. One can preview images and check the other files one after the other with their file names. Different catalog have all recoverable files, so, if deleted files are found, simply click recover button to save deleted files.
2. The other way to recover files for android device is, take out the CF card or SD card from device, attach card to computer system with the help of card reader and then execute CF or SD card recovery process.