Is it the songs you bought off itunes that don't work or all of them?
For a while the songs I bought off itunes wouldn't play, it would just skip right over them. All the other songs were fine it was just the ones off itunes that wouldn't work. I couldn't figure out what was wrong with it so I hooked it into the computer and it updated it. After that it was fine, all the songs would play, but then about a week later it would happen again. It was an ongoing cycle for a pretty long time but eventually it must have fixed itself because it hasn't happened in a few months.
So, have you tried hooking it into your computer and updating it? That worked for me to get the songs to play. I'd try leaving it hooked into the computer for a while and see if that does anything..