Microsoft has indicated that Xbox Live is currently experiencing a service disruption that affects logging in, Xbox Music and Video with no timeline on when it will be resolved.
Microsoft’s Xbox Live service is a core component of the Xbox 360 experience and will also be deeply integrated into the Xbox One experience too. While the service does not often face an outage, when it does go offline, it severely limits the consoles capabilities.
Microsoft is not offering a timeline for resolution but seeing that they are acknowledging publically that there is an issue, it means that they are working to restore the service to full capacity.
[Update] As of about 3:30PM EST, service has been restored.
Source: Xbox Live Status Page