iTunes store rejects my Apple ID

Hi. My Apple ID and password successfully get me into my account area (and this forum!) but not into the iTunes store.

When I try to sign in to the iTunes store, my Apple ID is rejected. I get a message saying "This Apple ID has not yet been used with the iTunes store. Please review your account information." So, I click "Review". Then I am told to create a new account (even though I already have one}. If I hit review, Then I am asked for credit card data. Why would it ask for credit card data BEFORE I have a new account? So I hit cancel, and we're now back at the issue in my first sentence--

Hi. My Apple ID and password successfully get me into my account area (and this forum!) but not into the iTunes store. Why is this happening?