Xbox One owners unable to sign in to Xbox LIVE; Microsoft looking into issue
Microsoft is looking into issues preventing Xbox One owners from signing into Xbox LIVE. Xbox Support acknowledged the problem via Twitter, assuring gamers "We're on the case to get this issue fixed as soon as possible!"
According to the Xbox LIVE support site, both Xbox LIVE Core Services and Social and Gaming services are "limited." Apparently signing into Xbox LIVE and joining other Xbox LIVE members in online games are both experiencing problems, though Microsoft has said they've resolved the matchmaking issue with Titanfall and Forza 5.
Unfortunately, signing into Xbox LIVE still remains a problem on Xbox One. We'll be sure to let you know once the problem is fixed.