Restarting your computer should cancel tune up. Try checking your hard drive for errors then run tune up again. How to check a hard drive for errors - http://support.microsoft.com/kb/315265 If the issue persists please contact support. How to reach support - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
Jim