Can't Join ANY Servers

I should be able to join my servers on my computer (for Minecraft) but I am not able to. It says "Mojang servers are down, but you can still connect!" Then I click on the server and it says "We cannot let you join because you are not on the same computer you logged on before!" or "Failed to login: The authentication servers are currently down for maintenance."

Thank you and please fix this!
Abigail
TheEndergirl