The login and session servers are down. This is why there needs to be an offline button. Not for pirates, but for the community that has to put up with the Sunday server nonsense that happens 52 times a year. The servers are ALWAYS down on Sunday. If you want to check on its status to see if you can quickly get in when the servers go up for about 10 seconds in an hour, google "is minecraft down?" Its the one at the top that says Xpaw as the domain (thats the best way of checking as it auto refreshes).