It looks like your account has been disabled by Gmail.
Google reserves the right to disable or suspend accounts when there is a violation of the terms of service and to terminate an account with or without notice.
You may wish to read the terms here: https://www.google.com/intl/en/policies/terms
Please start by reviewing the relevant Terms of Service. Then, if you think your account has been disabled by mistake then you will need to appeal Gmail's decision.