Hi, I'm getting a similar error. I've had a board at
for years. I didn't personally change anything, but am now getting this error:
SQL ERROR [ mysql4 ]
mysql_connect function does not exist, is mysql extension installed? 
An sql error occurred while fetching this page. Please contact an administrator if this problem persists.
Judging from other comments, I assume that I should try changing mysql to mysqli in the config.php file?
UPDATE: I've tried this and it seems to work. The board is back online anyway.
I seem to be running version 3.0.12 with a warning that it's out of date.
There's also these warnings:
HTTP input character conversion is improperly configured
mbstring.http_input must be set to pass. You can check the current value on the PHP information page.
HTTP output character conversion is improperly configured
mbstring.http_output must be set to pass. You can check the current value on the PHP information page.