my purchased songs aren't playing anymore. why?

Kait, sometimes an easy fix for this is to de-authorize the computer in iTunes/Advanced menu, then to re-authorize it. You do this by playing one of the songs purchased from the iTunes Music Store in iTunes. It should ask you for your Apple ID and password, then the computer will be authorized again. Sync you iPod with iTunes, and those songs should play again.

Another common cause of this is not having the latest version of iTunes (4.9).

I had that problem half an hour ago and i just took the songs off the ipod and put them back on, that normally works or playing it in itunes but on the ipod(ipod in source list, playing song in ipod via computer)