Are your computer is installed Vista OS? And are your iPod connected to it? Then your iPod could be in danger.
Do not simply use "Safely Remove Hardware" feature or disconnect the iPod using Windows Explorer.

Why ? That's because Vista OS has a bug that can corrupt your iPod if you're using that function. Microsoft didn't state what kind of problems will that bug bring to your iPod, they just say that, IF you're affected by the bug, you'll have to use iTunes to restore all the music on your iPod.

How To Fix My Vista ?
Microsoft has released the patch for the problem. You can now download the patch here:-
Vista Patch for iPod