Error Connecting to Database

I am totally baffled. I migrated my hosting to a new host. In the process we moved 16 wordpress sites. Some sites are up and running just fine. AND many are just blank pages. In reading all of the posts about this I made changes to the config file to make sure that the host, database name and password are all correct. I made the slighest bit of progress because now I get the error message.

When I sign into my php admin — the password and user name are different. When I check them against sites that ARE working they are different from the config file.

I’m just not sure what to do to fix this.

I have read many posts and can’t seem to figure it out.

Thanks for any ideas.
Donna