My daughter and I each have a 4th Generation iPod. Within the first year both had to go back to Apple for repair with the same fault. After the warranty period had expired, we both suffered the same fault again
The fault starts to show as an intermediate file system error, the one showing a folder and telling you to look on Apple’s web site for help. After some playing around (from various resets up to a complete reinstall), this was fixable for a few days. Then came the inevitable sad iPod icon. With more bits of fiddling around we could restore service again, but as time went on this became harder and harder.
Finally it became impossible to get the iPod to work. The symptom was very clear. The iPod would try to start, the disk would start to spin up, there would then be a series of clicking sounds from the hard drive, and it would die.
From the internet I gather that this is not as uncommon a problem as would be hoped.
My initial searches of the internet for what was wrong led me to a number of sites where people claimed experience of this sort of problem with hard drives. The bottom line was that the drives were faulty or damaged. One line was that the drive head mechanism was sticky, which is why the head could never locate the data needed to start. This sounded plausible. Tied to this was what appears to be quite a famous remedy, namely to treat your iPod like a dodgy TV and give it a hit. In fact this advice is quite well refined. Since the iPod contains a hard drive, and hard drives are relatively sensitive, this hit should not be too hard. Typically striking it into the palm of you hand seemed to provide just about the right level of sudden motion without being too hard on the drive. This advice worked for us for a while, but in the end it only kept the iPods going for a bit longer.
Then I pondered; typically when something works on being struck, it is typically a loose joint at fault. Moreover, I once had a desktop whose hard drive had a flaky connector which occasionally needed resetting. So I had a closer look at what people were posting on the internet, and indeed there are claims that the hard drive cables may be forming a poor connection. The only solution is to open up the iPod (see next note) and actually reconnect the drive cables. Typically you may not need to unplug, just wiggling the cable connectors in place is good enough.
With my iPod I only had to do this trick once, and it behaved perfectly well after that (and is still behaving). With my daugher’s iPod, I had to the this trick twice (but my excuse was that I had fiddled less with the connection onto the main circuit board on the first time).
I am 100% certain that the solution I have described is appropriate for most similar iPod problems, particularly for those that are fixed (temporarily) by a good whack!