Proceed according to the error message.

Wrong Password

You can activate the show password checkbox to see the entered password and make sure that the problem isn’t keyboard related, e.g. capslock is turned on.

You can request a new password when clicking Forgot your password? which is located under login button if email was set up.

No user with this name found.

Either you misspelled the username or the user doesn’t exist (anymore).

If there is a Forgot your password? link below the login you can request a new password with the email you are registered with. With the new password you’ll also receive your username.

This user is not activated.

Your user was deactivated. If you think this to be a mistake please contact your project manager.

Too many login attempts.

For security reasons (e.g. automatic attacks) the login gets locked after a few failed attempts. Number of failed attempts and minutes to wait until you can try again depend on project specific settings but in most cases you can try again after a few minutes.