Error establishing a database connection

I have just created a site, all was ok, I then installed phpBB.
During the install I changed my password on my database, as the phpBB said the one I had entered was incorrect, the phpBB works ok but on WP I get the error message Error establishing a database connection, is this because I changed the pw on the DB? if so how can I correct this, I do not know what the original pw on DB was.

Trevor