Walter, I understand the first part - OneCare won't start, but I don't understand the last part of your sentence, which doesn't appear to be a question.
Is this a new installation or did OneCare stop working? What is the exact error message you are getting? If this is a new problem and OneCare was working before, has anything changed? New or updated software or new hardware, for example?
One thing that you should check is the PC date and time. Make sure that it is completely correct - month/day/year and time. If it has somehow been changed, OneCare can fail to run.
You can also contact support:
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve