Songs don't play properly (or at all)

Recently, a few songs on my iPod started having problems when playing. They would get to a certain point, and then the iPod would freeze for anything up to a minute or so, then play for a few seconds, then freeze again, and so on. During the frozen time, the display would show that the song was playing, but the time did not change and the iPod did not respond.

Since then, more and more songs began having that problem, until in the end I decided to restore the iPod. I did that (with the most recent software), and had more problems. Songs would no longer transfer to the iPod (the transfer would get stuck after a few songs, and would eventually stop. Then no more songs would work). I have tried restoring it several times to fix that. The last time I tried it, the song transfer worked fine, but the iPod will still not play songs properly. It is currently frozen (as it keeps doing) and iTunes is not recognizing it, although it is connected to my computer. I can feel (and hear) the hard disk moving too.

Any suggestions as to what might be wrong, and how to fix it?