Can't add PayPal as form of payment

I've done it before, but now I can't add PayPal as a form of payment to my iTunes account. the "PayPal" icon never gets highlighted when I select it. I go through all the steps and when it comes down to "continue to iTunes Store" it goes to the Apple web site, which wants me to download iTunes which already up and running, instead of iTunes on my computer, which is already open.