Problems adding the blog

I tried installing it. I have an Invision Forum 2.0 already installed and only 1 mySQL database, someone told me I can do more than one thing on 1 mySQL database, is that right? I tried to do it and used the same db user / pass and db name and everything but it still gave me the “Error establishing a database connection” page. Is it because i have an invision forum on there already? i tried with local host and then tried with the actual host name it says for my database. It is the same stuff i used to make the invision forum and that worked, can someone help me out? thank you!