Same problem here, except my situation a bit better. Everything starts up normally, until you press continue. You see the loading screen and poof, you're in the desktop. It didn't happen in the past and started acting strange recently.
Is the account on your computer the same as your Xbox live account that's linked to the service. By computer account I mean i.e. Admin or local. Make sure for which ever you have it's the same as your Xbox live account.