Please contact support for help with OneCare or, as Jim noted, provide specific information about your problem such as error messages encountered and what you are trying to do. Note also your operating system and if this is a new install or reinstall for you.
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 Forum Moderator