When you say that you attempted to activate, how far did you get in the process? You would need to login with a LiveID, then provide payment information, and then complete the activation, which is the receipt of the subscription credentials from the servers.
Do you have any other security software installed that may be blocking communication with the server?
Are you using Internet Explorer or another browser?
Now that you have reinstalled the trial, set IE to be your default web browser in Set Program Access and Defaults in Control Panel. Open IE, clear temporary Internet files, delete cookies, and on the Connections tab, LAN button, uncheck "automatically detect settings."
Close IE.
Open OneCare.
Click on the subscribe link and log in with the LiveID you purchased with. You can confirm the status of your subscription at http://billing.microsoft.com
If it still does not activate your installed copy, please contact support (via email as a trial user, per the FAQ)
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve
