I bought my xbox (250gb) with kinect earlier this week. I have had a few problems with connecting which I won't bore you with, as seem to be resolved now. However, during these issues, I created my xbox live account vis my computer. I now want to sign into that account with my xbox, but the only option I can find is to "Join now" which the system thinks I want to create a new account. If I use my log in details it tells me that there is another gamertag with those details, and to use a different email address etc.
How can I sign in using my existing acct?