I used to have the same problem you use your
MINECRAFT.NET username and password go to
MINECRAFT.NET make sure you say forgot password and username to reset your password and find out your username go to your email get your password reseted then go to mineshafter login with your email username and password hover over your name or username you have present after you login to mineshafter go to setting and put in your
MINECRAFT.NET password and email to where it says connect account then download the proxy and server proxy open the player proxy type in your
MINECRAFT.NET username and password click the top button over login click update it will say WILL FORCE ( that mean it's done ) click done click login it will load and your done
(P.S. if it crashes that means you need to get and have Java SE 6 on your computer)