When Circuit City gave you the PC with the installed and activated OneCare, they should have given you a form with the subscription LiveID and the password.
Assuming that you don't have that paper, you have two choices to renew - contact support to get the password reset and then proceed to purchase a renewal at full retail price....
Or, purchase a new retail copy of OneCare in a store or from an online vendor such as Amazon.com and use the Key to start a *new* subscription with a LiveID of your choosing. (this option is cheaper. Your PC will remain protected for about 30 days after OneCare expires, getting updates, but you won't be able to configure it or run manual processes, plus it will nag you)
If you choose the second option, uninstall OneCare (
How to Uninstall Windows Live OneCare )and reinstall from
http://onecare.live.com (the trial download) and activate by opening OneCare, clicking Subscribe, and signing in with *your* LiveID (
http://account.live.com to create one) and then selecting the option to activate with a retail key or PIN.
And, yes, the process is more convoluted than it should be.
How to reach support (FAQ) - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
-steve
Microsoft MVP Windows Live / Windows Live OneCare & Live Mesh Forum Moderator