iTunes won't let me buy a song

Hi, I have an oddish problem I'm hoping someone can help me with: I can't seem to purchase anything on iTunes. When I click on the "$1.29 BUY" button... nothing happens.

I can download things for free, like podcasts. I can also purchase songs via iTunes on my iPhone.


I'm using iTunes 9.2.1 on a MacBook Pro i5.

Any ideas? Thanks.