Why won't the Itunes store allow me to buy anything?

The Itunes store won't allow me to buy anything. I'll click on a song or tv show episode I want to buy and click on the normal cost button, but nothing shows up. It won't tell me anything. I've checked the right amount of money, I've tried to update my itunes to the newest version but my computer seems to be coming up with more. I'm not really sure what's going on with it. Has anyone else had this problem? Can anyone help?

I would really appreciate it.

~ATC