So you get the same error as when you run the CGI? Then it seems that your Perl isn't able to find the module that you say you installed. Perhaps it was installed in the wrong place, or your library path is wrong.
It sounds like you need to address the root cause -- is the MySQL client side software loaded? Can you access MySQL from the command line?
I can access the mysql from the command line, execute the commands, output is as expected in the terminal "perl hello.pl" but the same script fails with in the browser "http://localhost/cgi-bin/hello.pl" with the error message posted int he first thread.