Why can I not play music I have paid for?

About 2 years ago, for the first time I bought an album from the itunes store on the same computer I currently am using. I was able to listen to it fine. I don't reguarly download from the itunes store, but the music that I have done, for some bizarre reason, I now am refused access to. I cannot figure it out. At first it refused my password (which I was so sure was entirely correct, but nevermind) so I changed it successfully.

I went back to itunes, trying to just simply play a song, and I'm asked again for my password, so I keep entering it, and it says:

'this computer is already authorised. Incuding this one, you have authorised 2 computers out of your available 5'.

This is odd, as I bought the music on this account, my only account, on this computer and have only played it on here. Anyway, I respond to this message with the only option available 'OK', and then I proceed to play the song...but I am asked for my password again, and so I enter it again, and the same message comes up again and I press OK again...and again and again. It is a short and unsatisfying circle with no escape.

I do find apple really quite frustrating sometimes. I paid for music I can't listen to. I would have preferred to pay an extra £3 for the CD to listen to how I wish, on many computers, disc players etc, to avoid the hassle and controlling nature of these programmes. RANT!

Please please help?

many many many thanks : )