I cannot download music from itunes on computer (Dell) to my older ipod now ( have done so numerous times before though). I get a warning "files can't sybnc> view sync problems, but then the message says ' all actions are complete.

I am unable to download music I've purchased from the itunes store to my ipod (version 4.2.1), It shows up on my computer in itunes (Dell) and it works on my iphone, but can't get it to download to my older ipod. A warning comes up "Files can't sync > view sync problems, but when I view sync problems, it says "all actions are complete. Your files are up to date." Still not showing up on my ipod though.