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.
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.
Again, the details of the banning algorithm are secret, but it's been strongly hinted by SE staff that if you're banned from asking questions, posting some good answers may help get you un-banned.