If you have an active subscription, which is what was created when you activated, you need to use the same LiveID to renew.
If you don't recall the LiveID you used for your subscription, you will need to contact support who can provide that information to you using your Key and/or contact information.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
Alternatively, sign in at http://billing.microsoft.com with email addresses that you have set up as LiveIDs and one will show your subscription listed - and you will then be able to renew.
If you know the LiveID, but don't know the password, and had set up an alternate email address for that LiveID, you can reset the password at http://account.live.com.
Since we're talking about a renewal, it may be simpler to abandon the existing subscription and create a new one with a new LiveID, either purchasing a new online subscription with a credit card or using a retail key from a boxed copy (which may be cheaper for you, anyway...). Just uninstall OneCare when it expires, then install again and activate/subscribe with the new LiveID - *and* make a note of the LiveID and password.
-steve
