Problem with wireless keyboard, mac book pro and cinema screen

Hi

Hope this isn't too daft a problem but I have just purchased a Thunderbolt cinema screen to make using my Macbook Pro in the office a better experience. Whilst in the Apple store i thought the wireless keyboard would be the perfect addition to this set up.

I have tried following all the keyboard and bluetooth set up stuff and it does detect the keyboard but it will not pair.

Any tips gratefully received.

Thanks