Have you been running with PHP 5 enabled? If so, if your server was moved or upgraded, it may be back to PHP 4 even though cPanel (and the .htaccess entry) says "PHP 5". Back up your public_html/.htaccess file, and try disabling PHP 5 from cPanel and then re-enabling it. I did a quick search for mysqli in these forums, and problems with it not working seem to often be related to PHP 5 not being properly enabled. It's worth a shot...
Hi, thanks. That php5 setting solved the problem.
After removed php5 and installed it again, mysqli_connect() works.
Though don't know how it was disabled, it happened once before, long ago.
The site is back to normal, thank you.