I've tried all the solutions it lists on the apple site and nothing worked. I tried it in my dad's pc and it worked straight away, when I installed iTunes on my dad's pc there was an extra option check box (I can't remember what it was exactly) but it's not there for me when I install it.
I've also had problems installing new broadband on this system this week when again it worked on my dad's instantly.
I've never had any problems like this before, I think maybe this new house is haunted or something.