My Ipod Classic has suddenly started to freeze up when I try to skip to the next song in my playlist. When I hit the skip button it freezes for up to a minute, and when it starts to play again it has often skipped 5-6 songs. It also refuses to play certain songs even though the same songs play just fine in Itunes. I've tried to restart the Ipod itself by pressing the menu and center button, and I'v tried to restore the Ipod in Itunes. I run the latest version of both Itunes and the Ipod software. I don't know what to try next, so any help would be much appreciated.