inability to purchase songs from Itunes

It's been a while since I've purchased songs from ITunes. I have a PC and my PC Itunes library gets exported onto my IPod Classic. Today, I noticed I was "locked out" of my account for security reasons, but then I reactivated my Apple account and I also authenticated the PC. Still no luck purchasing songs, however. What gives? Do I also need to somehow update the billing information as well? If yes, how?