i bought cs5.5 in the past and am now trying to download it to my new computer, but cant seem to find the original disk for it. Though I have my Serial Number to allow the download. What can I do?

i bought the cs5.5 suite cd in the past and am now trying to download it to my new computer, but cant seem to find the original disk for it. Though I have my Serial Number to allow the download. What can I do in order to get these programs to download to my new computer without having to purchase them again!?!