Failed To Login: Bad Login

I logged in to Minecraft, and I went on to a server. It came up "Failed to login: Bad Login". I logged out of Minecraft and went back in and it didn't work. I tried lots of different servers to try and find out if the server was down but none of them were letting me login. All Bad Login. If it helps I'm running on Windows 8. Does anyone know how I can fix this? Oh and add quite a bit of detail, I'm not that great at stuff like

Thanks

COR301