The iPod is basically a portable media player which uses a hard drive to store data.
Like all media players, this too can get damaged or corrupted.
One can store music to the iPod by connecting it to the computer (Windows or Mac).
During this process the iPod must be connected continuously and while removing it one needs to ensure to first disconnect it from the computer by ejecting it.
If this is not done, often, all the data (songs, videos, pod casts, etc) get deleted from the iPod.
In such a case one can use an iPod Recovery Software to help restore all the original files back.
For instance, if while transferring files from your computer to your iPod, the electricity goes and your computer shuts down without allowing you to 'eject' the iPod.
All the files in your iPod would get deleted.
Cause: The iPod is synchronized to you computer just like an external USB device.
When you eject the iPod is disconnects itself from your system, however if you don't disconnect it, the sync is lost and the data gets deleted from your iPod as well as iTunes.
When the computer shuts down, the same thing happens, causing deletion of your files.
Solution: In some cases you can try and connect the iPod back to the computer.
If the data hasn't been erased from iTunes, you can re-synchronize the two and restore your data.
If this doesn't work you can download an iPod Recovery Software and use it to restore all your iPod data as before.
Once you have downloaded the software.
You can connect the iPod to the system and use the software to recover iPod data.