When I click sign in on the xbox.com home page I get to this page: https://live.xbox.com/en-US/Flows/AccountCreation/AccountInformation.aspx
It seems to be asking me to make a new account but I just want to sign in. Can anyone help me out?
IIRC if you haven't done it before, you need to log on to live through your 360 and link it to an MSN/Windows Live account first.
There are many great features available to you once you register, including:
Sign in or Create Account