If you are getting the message:
Sorry, we are no longer accepting questions/answers from this account
Then you need to see this question for detailed information on why you're banned and what you can do about it.
In short:
There is an automatic filter that will ban questions and/or answers from IP addresses or accounts with a history of extremely poor posts.
The details of the filter are secret, but it is partly based on downvotes. If your questions and/or answers are getting many downvotes, you are likely to be banned.
Deleted questions and deleted answers count towards the automatic ban. If a large percentage of your posts are deleted by yourself or the community, then apparently they were not suitable for the site.
In order to get un-banned, you need to edit some of your existing questions and/or answers to improve them.