If your mp3 files fails to play on the iPod or any other mp3 player, there could be several reasons. It could either be corrupted due to incomplete download, the headers could be truncated, there must be garbage at the start or end of the song, etc.
Mp3val is a free opensource tool that determines the problem in the mp3 file and then repairs it. The mp3 file that fails to play on a device is not necessarily due to incomplete download, instead of deleting it you should scan and repair it using this tool.
The usage is simple, first go ahead and add file(s) or folder(s) and then select Scan All under the Actions menu. Now once the problem is detected, select Repair all files under the Actions menu.
If you want to find out the reason of the problem, select that mp3 file and the problem will be described in details(see the red marked area in the screenshot above).
Once the files have been repaired, it creates a backup of the original mp3 file in the same folder. So in this way your files are never lost and at the same time you get a working copy of mp3 files.
We would recommend that you scan your mp3 collection using this tool. I scanned a few songs and it found problems in two of them(again see screenshot above).
It is a portable tool and works on Windows XP, Windows Vista, and Windows 7. Enjoy!