Minecraft – Sometimes I get a message saying “Failed to Login” when opening Minecraft

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.

If you have a firewall it may be preventing minecraft from accessing the login servers. Try disabling it and logging in. If that works then investigate the settings to override the block of minecraft.exe or java.exe.