Failed to login

This text was translated with the Google translator because my english is really bad, so here's the
Translation:

I have not played Minecraft for several days and wanted to play again a few days ago. Unfortunately, when I want to join a server I get the message: "Failed to login: The authentication servers are currently down for maintenance.". so far so good ... But if I join from the same PC with the account of my sister on the same server, it works bound free. This error is not only on this one server but at all. Error occurs on all Minecraft / Server versions.