I trust that you mean that you activated the first computer with a LiveID and then entered the key code from a retail box. On the 2nd and 3rd PC you activated with the same LiveID. You would not have been able to enter the key again after the first attempt.
Now, on the PC that is in red status, open OneCare. The main window for the program will explain why you are "at risk" and what you need to do to resolve it. If you need help, contact support.
How to reach support - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve