Sounds like the contentdb you deleted contain the site you are looking for. Why did you delete it? Nothing wrong with having multiple content dbs for a web application.
Regarding "default conentdb", you can set a particular content db to be the "default" db used when creating new site collections. You do this on the same screen that you used to add content dbs. You can either set the "Database status" to disable or set the maximum number of sites to the current number of sites.