So, we've all had problems getting on to servers today. You might be blaming your internet, or your minecraft, or <insert reason here>. But, it's not just you. We're all having the same problems. Mojang is having some issues with their servers, which is not allowing anybody to join any MInecraft servers. We should be back soon though!
You can check the status of their servers yourself here: http://xpaw.ru/mcstatus/