Q: My computer's iTunes won't let me login, but I can on other devices.  No login screen appears in any attempt I make on iTunes.

I can't log into my itunes 12.3.3 account on my mac book pro running el capitan. I also wasn't able to log into the account on another user account on my mac or when running Yosemiti. If I turn off my firefall and security for my mac and computer, respectively, I'm still not able to log in, as in, I'm never taken to the login screen, but I can still browse the store. As a result, I can't listen to any of my purchases items. I can still log into my account on my phone and other computers. What's happening?