Once the domain is removed, you nolonger controls the resources associated to it like mail ids.
Add the old domain as parked or addon domain and delete the old mail ids then remove the domain from the parked/addon domains.
It depends on which cms or blog you are using?
Every blog or CMS software has its own procedure to change their domain URL.
Try to find that first.
One more thing is when you set the name servers for the domain . It may take upto 48 hours to DNS propagate, Till then the site may not be...
The database username must be in the format of cpanelusername_databaseusername
and also the databasename too in the format of cpanelusername_databasename
To terminate your hosting account, Please fill this form
By the way your account suspended for inactivity. You can unsuspend yourself from account panel.
What are the details you are trying to give?
They should be like this format.
Database : localhost
DatabaseName : cpanelusername_databasename
DatabaseUserName: cpanelusername_databaseusername