Can you open onecare from the programs list? (Start>All Programs)
Does onecare give you any error message?
Verify through add/remove programs in control panel, if onecare is listed, if not present you might need to reinstall it.
If onecare will give you any error message. Try contacting support.
How to reach support (FAQ) -
http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2