Xbox LIVE is currently down to unforeseen technical issues.
Microsoft has announced that Xbox LIVE is currently up and running, after technical issues made it stop working a few hours ago.
Users should be able to log in without a problem. Microsoft has yet to announce what caused the issue. You can check at http://support.xbox.com/en-US/xbox-live/browse?xr=shellnav for the latest Xbox LIVE status.
- Xbox Live is down, Microsoft investigating cause (theverge.com)