If you have One care installed on another computer, open One Care>Help>About Windows Live One Care and you will see the Live ID associated with your subscription. If you are unable to do this or find your Live ID but can't remember your password you will need to contact support for help. How to reach support -
http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
Jim - MVP Windows Live - Forum Moderator - Live One Care - Live Mesh