I cannot sign in

Almost every sign-in problem is one of these four, and they look identical from the outside.

1. You are typing your callsign. The sign-in box takes the email address you registered with, or your login name. Your callsign is a different thing: see Your login name is not your callsign.
2. The password is wrong. Reset it: see Reset your password.
3. The game is older than the servers allow. If your build is too old to connect, the game says so and points you at an update. Let the launcher finish patching and try again.
4. The account is banned. You will be told that it is, rather than getting a wrong-password error. You can appeal: see Banned or muted.

An unverified email address does not stop you signing in. If you never got the verification mail you can still play, and you can fix it later: see I never got the verification email.

Still stuck

Open a ticket. You do not need a pilot or a working game to do it, only the account. Tell us the email address you registered with and what the screen said, word for word.