I had this problem too. When I logged in it brought me to the page where I had to enter my contract number and pin code. I haven't used that pin code since the first time I registered and have no idea what it is now.
I called member services and the woman on the phone was not very helpful. She kept trying to tell me I was already logged in. I had to explain the problem several times before she finally got a supervisor and they reset it for me. I have no idea what happened, but it was very frustrating! I can get in fine now though. You may want to give MS a call...