How do I play a song from the iTunes store?

I cannot play a song in the itunes store. I have been able to before now. I click the song and it says in need to authorize this computer and when i go to do that, it says "There was a problem storing your authorization in this computer."|||Have you used your account on 5 other computers?


if you have you'll have to un authorises one before it lets you play a song on the one your using.