I've moved your post to the Install topic folder.
If your password is longer than 8 characters, change it at http://account.live.com and then use the shorter password to complete activation.
What happens when you say you are unable to sign in? Are you getting an error message? What is your default web browser? If it isn't Internet Explorer, make that the default browser and try again.
If you are still unable to proceed, please contact support.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve