Just tried setting up the latest Apache (2.4.1 x86 VC10 from apachelounge) and PHP (5.4 VC9 TS X86, with the php5apache2_4.dll) on my PC and ran into this weird problem; in my php.ini I have enabled all of the following:
extension=php_mysql.dll
extension=php_mysqli.dll
extension=php_pdo_mysql.dll

but when I try to print the available PDO's using this:
print_r(PDO::getAvailableDrivers());

It gives me an empty array. PhpMyAdmin and MantisBT also refuse to work, saying that the mysql extension is missing.
phpinfo() gives this:
PDO
PDO support enabled
PDO drivers no value
and when searching for mysql, only the mysqlnd section pops up...
The DLLs are there in the D:/php/ext folder and no errors pop up when starting up Apache, as well as no errors in the Windows Event Log, and PHP itself has no error log anyway. What could possibly be the problem with this? Before this I had Apache 2.2.22 from apachelounge and PHP 5.3.9 and I had no problems. Now nothing works...