Minecraft – If I buy minecraft with a mojang account on a computer, do I need to buy it on another computer

First make sure that you're logging in with your email address, not your old Minecraft username. Everything uses your email address now that you've migrated your account.

If that's not the problem, this is simply an account bug that we can't help with. For account migration issues that aren't resolved by that help article, you need to contact Mojang support as it says at the bottom.

(No, accounts can't be un-migrated.)

There is a number of things you should rule out first:

• Are you able to login through http://account.mojang.com/login?

• Are you using the proper client from http://minecraft.net/download?

• If you were able to login with your old computer; make sure your current one doesn't have any firewall blocking internal / external connections.

• On the computer with the issue, do the following:

  : Go to this url, and substitute USER for your actual username and substitute PASS for your actual password.

  : It should output a Session ID (a bunch of numbers and letters), if not; and it returns Bad login or another exception; contact mojang.