"Authorized Computer"?

My son's iPad was recently disabled, I suspect from trying to access the restricted area to which he does not know the code. I went on my PC and downloaded iTunes and all that and after reading up on the problem I felt like my only option was to restore it and start over with uploading all the songs we'd bought over the years. That's when I was told my computer wasn't "authorized". Really?? That's all it said, no link to help on how to get it "authorized". I guess it recognized that this is a different computer than when I first downloaded iTunes a few years back on my old computer, but where do I go to tell it to disregard the computer I no longer have and am now using this one?? And why do I have to do that anyway?? I am logged in, it recognizes and accepts my account information, it knows it's me, why doesn't it accept the PC I'm using to do all this on???