There are a variety of reasons why you could have been banned from Warframe, including verbal abuse to other players, cheating, hacking or other violations to our Community Guidelines, Code of Conduct, Terms of Use or End-User License Agreement (EULA). We reserve the right to ban accounts when we see fit and the duration is up to our discretion.
For more information on why you might have been banned from Warframe automatically, please also see this Forums thread.