Database connection error

Hope someone can help?

Am i able to add a second wordpress site that sits on an addon domain?
I added a new database i the cpanel to link to the second site, this was successful and i started working on the second site. However, when i went to look at my site that is already running in the root i got the error ‘error connecting to the database’.

After looking around on google i deleted the second database and this still gave me the same error. I then deleted the one user from the root database, created a new one, amended my wp-config.php file and the old site was back up again. Would the second base added cause conflict with the first one?

Sorry if this is confusing, its all abit complicated.

Any help much appreciated. Thanks