We often receive emails from players who believe that, after changing computers, they have lost their Minecraft username or game. However, you can access your Minecraft account from anywhere where you have a copy of the game, or an internet connection to play from minecraft.net, regardless of which computer you play on. You cannot have a Minecraft profile deleted by playing on a different computer.
If your worlds are gone after changing computers, that is because world files are saved locally to the computer where they are created rather than being saved on your account. If you want to know how to move your worlds from one computer to another, please visit our help article, Transferring Minecraft: Java Edition to Another Computer.
If you are having trouble logging in and are being asked to answer questions, visit our article on Account Security Questions.
If you think that your account has been compromised, visit My Account was Stolen.
If you cannot log in, make sure that you are typing your email or username exactly as you had it before. Note any underscores, letters replaced by numbers, or characters that look like other characters. If you are having trouble with your password, please visit our Change or Forgot Password article for information on how to change your password.
After trying these options, if you are still unable to log in, you can contact Minecraft support for more help.