again the Error establishing a database connection error

I have looked through the wp-config.php file and it is correct. The same username and password that I set my mysql database to.
The problem is that I have already set it up and it ran good for 2-3 weeks, but then I decided to register another domain with my server so I could run a second website. I made the HUGE BIGGEST mystake in my life to delete some of wordpress files thinking that they are on another server with my second domain, after I realized they both shared the same server I reuploaded them and it cant connect since then.

I still have my database with all the files from my old wordpress site and also the wp-content folder with plugins, theme and such.