Error establishing a database

I have recently gotten a domain with GoDaddy.com Then I added WordPress that they offered to my domain. Recently I could not get a WordPress Plugin to unzip and load, so I went to look over my data =base, had to set user password, but did not find anything there. I ended up going to my FTP to upload the plugin. Then, I was posting on WordPress, my free account, and found something that ask if I wanted to add my website or other blogs. Now my hosted domian shows in my free account as one of my blogs. And, I get a 500 error message, plus, “Error establishing a database connection”. I do not know what I did to cause this, but I messed up something. I contacted my hosting service, but nothing n the way of help as of yet. So here I am.