You have tried to change the PSN account without creating a new User account. You can not sign in to a different PSN account on the same User account, that is why you are getting the error message.
You need to put the original email and password back in the User account, then if you want to access another PSN account, you need to create a new User account (XMB > Users > Create New User > name it, then press X to log in to new User account), then add the PSN account (XMB > PlayStation Network > Sign Up for PlayStation Network > Use an Existing Account > enter your email and password, continue to follow on-screen prompts to finish setting up account.
If you only have one account on the PS3, and you delete that account, it will delete all content on the PS3. If you have more than one account on the PS3, the content will stay on the PS3, but any purchased content will not be accessible unless you put that account back on that purchased that content.
If you can't get your access your account after creating a new User account, then the PSN account got banned, or there is something wrong with it. Creating a new account will allow access to the games, as long as the old account is not banned and is on the PS3.