Locked out Mojave

Hi darrin112,

​Thank you for using the Apple Support Communities. I understand you're running into some issues with a password on your Mac.

To clarify, you installed macOS Mojave and you see an account called "Guest" when you start up, but it doesn't accept the password you were provided and you haven't been able to reset it. Is that right?

It sounds like the account in question may be an administrator or standard account that's labeled "Guest" rather than an actual Guest account; do you know if that's correct? Set up users, guests, and groups on Mac. Are there any other admin accounts on the Mac?

It sounds possible that FileVault is enabled if you're not able to use "resetpassword" in Terminal. Have you tried these steps from the resource titled Change or reset the password of a macOS user account?

"Reset using the Reset Password assistant (FileVault must be on)

If FileVault is turned on, you might be able to reset your password using the Reset Password assistant:

1. Wait up to a minute at the login screen, until you see a message saying that you can use the power button on your Mac to shut down and start up again in Recovery OS. If you don't see this message, FileVault isn't on.
2. Press and hold the power button until your Mac turns off.
3. Press the power button again to turn on your Mac.
4. When the Reset Password window appears, follow the onscreen instructions to create a new password.
5. If you need to connect to Wi-Fi, move your pointer to the top of the screen and use the Wi-Fi menu  to connect. To exit without resetting your password, choose Apple menu > Restart.
6. 
7. When done, click Restart.
8. If you were able to reset your password with the Reset Password assistant, log in to your account using your new password.
9. Determine whether to create a new login keychain."

I hope these steps are helpful! Have a good day.