Help!!! Database error on the online server

[eluser]chamu_cfi[/eluser]
Hello! I have been using 1.5.4 on my pc CI on Windows XP SP2 and XAMPP. The problem arises when I upload the project on my server "Datattec.com" in Argentina, the default CI controller loads sucessfully, but with database transaction get the following error: "
An Error Was Encountered

Unable to connect to your database server using the provided settings."

You do not need too much code for that to happen, it is enough to write the next line "$this->load->database();"

I'm trying now with CI16 and get the same error.
I also tried to change the php server version 5.2.0 to 4.4.4 and nothing.
Don't know if it's important, mysql server is "MySQL 4.1.22-standard".
I have others applications running on this server like dotProject and I have no problem.

I don't know what to do.
I would appreciate any help, ideas, url or anything

PD: Sorry, my english is bad, I did the best that I could.