It looks like Microsoft is experiencing some issues with Xbox Live sign-ins again, with the Xbox Live service status page indicating issues across all devices, including the Xbox One and Xbox 360. It looks like the issue has been ongoing for about two hours now, but Microsoft is aware and working on a fix, stating:
"Having trouble signing in to Xbox Live? Our team is working to get this fixed ASAP. Thanks for your patience while we get everything back to normal. We'll update you as soon as we know more!"
So, if you're having trouble getting your game on, just sit tight and the issue should be resolved soon enough. In the meantime, might we suggest giving our Window 10 review a look while you wait?