The most common reason for the "not working" situation with OneCare is that the computer's date and time are incorrect. Right click the clock in the system tray and check the month, day, year carefully. Correct it if wrong and reboot.
If that does not resolve it, please contact support.
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|MS Security Essentials Forums Moderator ~